What is the best blind or shade system for a glass sun room

The Question Assumes Three Products Compete. They Are Three Positions.

A glass sun room is the only room in a building where the walls, the gable and most of the roof are the same product, bought from the same supplier, in the same order. That is also why the shading question is harder here than anywhere else in the house. There is no wall left to screw anything into, and the surface doing most of the heating is the one above your head.

Almost every comparison article answers the title by listing products: roller, roman, cellular, pleated, venetian, vertical, shutter. That list is real, but it is the second-order question. The first-order question is simpler and much less often asked: on which side of the glass does the shade sit?

There are only three answers, and physics ranks them before anybody picks a fabric. Everything after that is a refinement.

That first table is the whole ranking. The remaining sections explain why the ranking exists, what it costs to ignore, and where the sun room specifically breaks it.

Three Published Numbers, and They Come from a Roof Window Maker

You do not have to take the ranking on faith. One roof window manufacturer built eight identical test rooms, gave them the same roof windows and the same exposure, and measured what happened with different shading accessories. The published results give three numbers for the same window.

Three things in that table deserve to be said out loud, because the shading industry rarely says any of them.

First: a fully closed blackout blind still admits 0.37 of the sun's energy into the room. The word "blackout" describes visible light. It does not describe heat. The fabric absorbs a large part of the energy and gives it back to the room.

Second: the external blind is not marginally better, it is in a different category of better, and the gap is not fixed. It depends on which fabric you pick, by a factor of more than three.

Third, and this is the one that matters most for a sun room: these numbers came from a roof window manufacturer, not a blind manufacturer. The company that sells the glass went to the trouble of measuring what happens when you put fabric on either side of it. Almost nobody in the fabric business publishes the same comparison.

What Those Three Numbers Actually Say (Our Arithmetic on Them)

The three published values are enough to work out the whole ranking by division. The arithmetic below is ours, run on those three numbers. If your glazing build-up differs, rerun it with your own g-value instead of 0.61.

Look at what the ratio column is doing. The same three published numbers support "roughly twice as much heat rejected" and "up to about nine times less heat admitted", depending on whether you divide the energy that was kept out or the energy that got in, and which end of the fabric range you take.

Both statements are honest arithmetic on the same data. That is precisely why a fabric swatch will never settle the argument, and why the ranking has to be fixed by position before the fabric conversation starts.

The Long-Wave Trap: Why an Internal Blind Can Only Ever Win Part of the War

The mechanism is short enough to state in one paragraph, and it explains every number above.

Sunlight arriving at glass is mostly short-wave radiation, and glass is largely transparent to it. The energy passes through and lands on whatever is inside: a floor, a sofa, a table, or the fabric of an internal blind. That surface heats up, and a warm surface radiates. But it radiates at long wavelengths, and glass is far less transparent to long-wave radiation than it is to sunlight. So the re-radiated heat is now on the wrong side of the only exit.

This is the greenhouse effect, and it is not a defect in the blind. It is arithmetic. An internal blind can be perfectly made, perfectly fitted, and perfectly rated for its own purpose, and it will still be standing inside the room while the energy arrives.

An external shade never has this problem, because there is nothing to trap. It rejects the energy while the energy is still outside the building.

A second, independent path says the same thing in different units

The test-room figures are transmittance values. A separate body of work cited by a shading association monitored real rooms through a summer and recorded operative temperatures instead: roughly 47.5 degrees Celsius with no shading, about 32 with an internal roller blind closed, and about 28 with an external venetian blind. The reported reductions across the study were about 8 to 13 degrees for internal shading and about 12 to 18 for external.

Run the same division on those and the ratio comes out at about 1.26 times, not two and not nine. The two paths are not contradicting each other; they are measuring different things. One measures the fraction of solar energy that crosses a glazing assembly, the other measures how hot the air and surfaces in a real room actually got, which depends on ventilation, thermal mass, orientation and weather as well.

The honest conclusion is narrower than a headline but more useful: external shading rejects more energy, internal shading is not useless, and the size of the gap depends entirely on what you measure. Any supplier quoting a single multiplier without saying what was measured is selling you a number, not a result.

"Blackout" Is a Light Word. "gtot" Is a Heat Word.

If you take one thing away from this article, take the second row of the next table.

European standard EN 14501 covers thermal and visual comfort for blinds and shutters. It defines three solar optical properties for a fabric, and they always add up to one hundred percent: solar transmittance (Ts, the part that goes straight through), solar reflectance (Rs, the part bounced back), and solar absorptance (As, the part the fabric takes in and turns into heat).

Then it defines the number that actually matters: gtot, the total solar energy transmittance through the blind and the glazing together. Not the fabric alone. The combination.

That matters because gtot is measured against four standardised glazings listed in an annex of the standard, and the reference glazing is called glazing C, with a U value of 1.2 W per square metre kelvin and a g-value of 0.59. So a fabric rated on glazing C is not necessarily rated on your glass.

Note where the class boundaries fall. An internal blackout blind that measures 0.37 on reference glass sits in Class 2, and it is only one class boundary away from Class 1. The external awning range, 0.04 to 0.14, sits entirely inside Class 4. The class table is the shortest possible statement of the ranking.

Absorptance Is the Property Nobody Puts on the Swatch

Here are three real internal blind fabrics from one supplier's published range, with their optical and thermal values as listed.

Now do the one division that changes how you read a swatch book. The first and third fabrics are both sold at three percent openness. Their solar absorptance is 39 and 18. Two fabrics with the same nominal openness differ by a factor of about 2.2 in how much solar energy they take in and turn into heat.

The reason is visible in the reflectance column: 51 versus 80. The metallised back is not a colour choice. It is a thermal decision that happens to be printed as a finish.

There is a second, sharper division hiding in the same table, and it is the most useful line in this article.

Compare moving down the fabric list against moving across the glazing list. Changing fabric on reference glazing C moves gtot from 0.40 to 0.31, a spread of 0.09. Changing glazing from C to the solar-control glazing D moves the same fabric from 0.40 to 0.26, a spread of 0.14. Across the three fabrics, the glazing change moves gtot by 0.07 to 0.14.

The two levers are the same size. That is the whole point. The fabric is roughly half the decision, and it is the half that gets printed, sampled and sold, while the glass build-up is the half that gets decided in a different meeting by different people. If you spend the shading budget on the fabric and leave the glazing build-up to whoever filled in the window schedule, you have spent the entire budget on half the problem.

Openness Factor Answers "Can I See Out." It Does Not Answer "Will It Get Hot."

Openness factor is the share of the fabric area that is hole. It is the standard way to describe a screen fabric, and it is genuinely the right dial for one thing: how much you can see through it.

The trap is that openness factor feels like a performance number, so two fabrics with the same factor look equivalent. They are not. Look back at the two three percent fabrics in the previous table and read the Tv column: 7 and 3. Since transmitted light equals the openness factor plus the diffuse part passing through the yarn, the grey screen passes about four percentage points of light through the yarn itself, while the metallised black one passes essentially none. One glows, the other does not, and both are labelled three percent.

So ask for three numbers together, never one alone: Ts, Rs and gtot, plus which standard glazing the gtot was measured on. A data sheet that gives you openness factor and colour but not gtot is asking you to buy on appearance.

The Roof Is Not a Window, and Almost Every Sun Room Spec Treats It Like One

Here is where a glass sun room parts company with every other glazed room, and where the "best blind" question genuinely changes answer.

In a normal room, the roof is opaque and insulated, and the glass is vertical. Vertical glass gets its peak load when the sun is low, which is also when it is easiest to shade with an overhang or an external blind. In a sun room the roof is the glass, the sun is overhead at the worst hour, and there is nothing above it to attach anything to. The surface with the highest load is the surface with the fewest options.

It gets worse. Hot air rises, so the hottest air in a glass room is at the apex, which is the part you cannot reach by hand. A roof blind that needs daily operation is a blind that will be left in one position, and a blind left in one position is a fixed shading coefficient you chose by accident.

Specialist suppliers of overhead shading are unusually candid about this. One describes a horizontal roof blind as a system engineered to do a single thing, which is defy gravity, and explains that zip-type edge retention exists to stop the fabric drifting sideways, telescoping off the tube, wrinkling or jamming in the side channels, not to keep it flat.

The same sources describe a failure mode worth knowing before you buy: constant-tension spring systems provide their least pull exactly where the fabric needs the most, because the springs lose force as the blind closes. Later torsion-based systems were introduced specifically to deliver several times more tension, and to hold that tension the same whether the blind is fully open, fully closed, or somewhere in between.

One published trade threshold gives you a sense of scale: above roughly 2.2 metres of blind width, or a lantern larger than about 6.5 square metres, fabric support ribs come into play. That figure is one supplier's own geometry, not a rule. Treat it as a prompt to ask your supplier where their threshold sits.

The apex is a maintenance item, and nobody schedules it

Because the highest glazing is also the least reachable, the blind at the apex is the one most likely to be operated by motor and least likely to be cleaned or inspected. Two consequences follow, and both are cheap to deal with early and expensive later.

• Access: decide now how the apex blind gets reached in year five. If the answer is a scaffold, the maintenance plan is fiction.
• Fabric life at high temperature: the cavity behind an overhead blind is the hottest place in the building. Ask for the fabric's rated exposure, not its appearance rating.

The Collision Nobody Prints: 50 mm of Air Versus a Flush-Mounted Blind

This is the part of the subject that no blind catalogue and no window catalogue covers, because each one only prints its own half.

Glass manufacturers publish guidance on thermal breakage. One major float glass producer lists the use of internal shading devices such as curtains, drapes or venetian blinds among the factors that influence it, and states the condition plainly: if shading devices are used, they must be placed away from the glass to allow for a free flow of air at the glass surface. The same source lists other contributors, including frames in contact with concrete, excessive coverage of the glass edge by the frame, and films applied after installation.

Window manufacturers go further and put a number on it. One European window company's published guidance on thermal stress gives a safe minimum distance between the glass and blinds or curtains of 50 millimetres internally, and adds that if blinds or curtains sit closer than 50 millimetres, thermally toughened glass should be used for the internal pane. It also says what happens next: thermal stress breaks are not covered by the warranty of the glass.

Now look at what the blind industry sells as the best answer for an opening sash. Framed clip-in systems such as the perfect-fit and INTU type are routinely described as sitting inside the glazing bead, held tight to the glass, moving with the sash in both tilt and turn, with the handle operating in front of the blind. Flush is the selling point.

Flush is exactly what the glass manufacturer's clearance rule is warning you about. A blind that sits in the beading against the glass has a gap measured in millimetres, not in the tens of millimetres the glass maker asks for. Both statements come from reputable sources. Neither is printed next to the other.

We are not saying the flush-mounted system is wrong. It may be perfectly acceptable with the right glass build-up, and glass makers publish heat-treatment guidance precisely so that the combination can be made to work. What we are saying is that the two requirements are never printed together, and the exclusion clause means the cost of that gap does not land on the industry. It lands on whoever placed the order.

One more detail from the same guidance, because it is the kind of thing that only shows up after the fabric is chosen: where an integrated blind is sealed inside the glazing unit, the guidance calls for thermally toughened glass, both panes in a double unit and the internal plus middle pane in a triple unit. The reason is the same as above. Sealing a heat-absorbing device into the cavity removes the airflow path entirely.

Between the Panes: It Solves Dust and Cords, and It Moves the Failure into the Glass

A blind sealed inside the insulated unit is the tidiest answer to two real problems at once. It never needs dusting, because it never meets dust. It has no dangling loop within reach of a child, which matters more than most specifications admit: safety guidance in the UK advises against fitting a blind with a looped cord or chain in a child's bedroom at all, and internal blinds fall under their own child-safety standard.

The trade is not subtle once you write it down. A sealed unit is a single component. If the blind inside it stops working, you cannot open the unit to fix it, because opening the unit destroys the seal. So a shading failure becomes a glazing replacement. That is a bigger, slower and more disrupting event than swapping a blind, and it usually involves a different trade from the one that fitted the blind.

The published repair guidance for sealed units is consistent on this: the distinction is access. Some designs allow a removable interior panel or a swappable operator, and those can often be reset, restrung or have a tilt part replaced. Sealed units cannot be opened without destroying the assembly, so the practical path is to fit a replacement insulated unit, which in most cases does not mean replacing the whole frame or sash.

There is also a symptom list worth keeping, because two of the entries are misdiagnosed constantly. A magnetic slider that moves with no resistance usually means the magnets have slipped out of alignment, not that the blind is dead, and a slow full-range reset often re-seats them. A blind that is crooked or stops at odd angles often means an uneven lift cord. Fog between the panes is the one that is never a blind problem: it means the seal has failed, the desiccant is saturated, and the unit is finished regardless of what the blind is doing.

Three Questions Decide Whether a Sash-Mounted Blind Fits. We Publish None of Them.

Everything so far has been about which family to choose. This section is about whether you can physically attach the thing to the sash you already specified, and it is where most sun room shading projects actually go wrong.

Framed clip-in blind systems work by gripping the glazing gasket or bead of the sash. Published guidance from blind suppliers is specific about the prerequisites: the frame needs to be uPVC or aluminium, and the gasket needs to be deep enough to take the clips. Timber windows and older frames usually cannot take it.

Our frames are aluminium, so the first half of that test is answered. The second half is not, and neither is the third question below.

The third row is the one that gets skipped, and it is the one that produces the most expensive mistake. A blind that clears the handle when the window is closed can still catch it in tilt, in turn, or somewhere in between. The published instruction from blind specialists is to test the blind operating through the full tilt and turn range before finalising the fit, and to note which side the hinges are on. That is a five-minute check on site and a multi-week problem if it is done after installation.

If the handle sits very close to the glass bead, published fitting guidance mentions handle spacer collars placed under the handle baseplate to create additional clearance. That is a far cheaper fix than discovering the conflict once the blind is made to measure, because a made-to-measure blind that does not fit is a made-to-measure blind you have bought.

The Weight Moves With the Sash, and the Weight Is What the Hardware Was Bought For

A shade fitted to an opening sash does not sit on the wall. It sits on the moving part, and from that moment on it is part of the number the hardware was selected against.

There are two routes to that same extra weight. An integrated blind is sealed into the insulated unit, so the glass unit gets heavier and the sash follows. A clip-in framed blind is mounted directly onto the sash, so the sash gets heavier without the glass changing at all.

The consequence is mechanical, not cosmetic. Hardware load ratings are per sash, not per window or per opening, and the rating is what the hardware was bought to carry. When you add a blind to a sash, you are spending part of a budget that was already spent, and nobody prints the remaining balance.

Our own catalogue illustrates why you should not try to do this arithmetic from memory. We publish per-sash figures for some sliding series, including a twenty-wheel self-balancing pulley system, and separately a driving capacity figure for a different heavy-duty series. Those two numbers are not the same measurement. One describes what the rollers carry; the other describes what the mechanism is capable of moving. Putting them in one column and reading top-down is the single most common way our catalogue gets misread, and it is the same mistake people then make again when they add a blind and start comparing the blind's weight against whichever number happens to be nearest to hand.

So ask for three things in the same email, in the same units: the rated sash weight for your series and configuration, the fitted weight of the blind system including its frame and hardware, and the difference. If the series does not publish a rated sash weight, the honest answer is that there is no published budget to spend against, and that is a specification problem to solve before choosing a fabric.

Four Surfaces, Four Different Problems

"A blind for the sun room" is not one product, because a glass sun room is not one surface. It is at least four, and they do not fail in the same way or get measured in the same units.

The door row deserves its own paragraph, because it is the one most often decided last. A sun room door is a traffic route first and a piece of glass second. If the shade is mounted on the panel, it travels with the panel, which means it adds weight to the thing the rollers carry and it can rattle in the wind. If the shade is mounted on the wall, the blind has to be raised every time somebody walks through, which means it will be left down, which means the room gets the shading you did not choose.

There is a third option that is easy to miss and worth naming: leave the door unshaded. In most sun rooms the door is the one surface where the shading value is lowest relative to the inconvenience, because it is the surface people are constantly operating. Spending the shading budget on the roof and the gable, and accepting an unshaded traffic panel, is a real specification decision, not a compromise.

Motorisation Is Not an Accessory. It Is a Cable.

The single most common error in overhead shading specifications is treating the motor as an option to be chosen at the end. In a sun room it is the opposite.

Overhead and high-level glazing is out of comfortable reach by definition. Published guidance for roof lantern systems is blunt about the consequence: normal hand operation of overhead glazing can be impractical or impossible to reach safely. If operation is impractical, the blind does not get operated, and a blind that does not get operated is just a fixed shading coefficient you arrived at by accident.

Motorisation then becomes a services decision, because motorised systems do not share a power arrangement. Published product information for roof systems is explicit that motorisation is not fitted as standard, that not every system uses the same motor, and that not every system uses the same power supply, with rechargeable battery and mains or hardwired options both in use, confirmed at survey. That is a decision about where a cable goes, and where a cable goes is a decision made before the finishing surfaces exist.

Note what those four rows have in common. None of them is a fabric decision. Every one of them is a decision that has to be made while the wall is still open. That is the real answer to the title question. The best blind system is not the one with the best fabric; it is the one whose power, fixing and access were settled early enough that the fabric choice is still available to you.

Eleven Things That Look Like a Blind

Part of the confusion in this subject is that the word "blind" covers several products that are not competing with each other at all. Some control light, some control energy, some control privacy, and some only control the look of the room. Reading the table below as a ranking would be a mistake; read it as a sorting exercise.

Two of those rows change the project rather than the room. A louvred roof is a second structure with its own loads, drainage and approvals. Switchable glass is a glass change, decided in the glazing schedule, with power and controls that have to exist before the frame arrives. Neither is a blind order, and both are frequently discovered too late.

Ten Questions to Send, With the Answer That Sounds Fine and Is Not

The fastest way to separate a shading supplier who has done this before from one who is selling fabric is to ask questions that have a correct shape of answer. The right-hand column is the one to watch for.

Notice that the useless answers are not lies. Every one of them is a true sentence about the product. They are simply sentences that cannot be checked, which in a specification is the same as not having answered.

Four Surfaces of a Sun Room, and the Four Things Only You Can Measure

Everything above comes down to four measurements that no factory can supply, because three of them are about the building and one is about how you live in it.

• Which surface, and at what angle. A horizontal rooflight, a pitched panel and a lantern facet are three different products. Say which facet, and give its angle.
• Bead-to-bead glass size and bead depth, per sash. Not the recess, not the room. The clip-in frame is made to the glass and clipped into the bead, and a few millimetres matter more than they would for a blind hanging loose.
• Handle projection and hinge side. Published UK guidance puts handles at roughly 30 to 50 millimetres of projection and asks which side the hinges are on.
• When the room is used. A glass room used mainly in the evening has a different shading problem from one used at lunchtime, and the difference decides whether motorisation is a convenience or a requirement.

Everything else, including the fabric, is downstream of those four.

What We Publish, and What You Still Have to Ask For

We would rather lay the gaps out in a table than let you discover them on site. The left column is what is in our published material. The middle column is what that number actually measures. The right column is what you still have to ask for.

One row in that table is worth pointing at directly, because it catches people who have read the rest of the catalogue carefully. Our heavy-duty sliding series lists both a sash width of 53 millimetres and a track height of 53 millimetres. Same number, same series, two completely different meanings. One is the visible width of the meeting stile. The other is how far you lift your foot. A blind supplier asking for "the 53" is asking for one of them, and it is worth making sure you are both answering the same question.

Six Cases Where the Answer Is Not a Blind at All

Common Questions

Can I fit any internal blind to a tilt-and-turn sash?

No, and the constraint is the sash, not the blind. Framed clip-in systems need a frame material they can grip (uPVC or aluminium, which ours is) and a glazing gasket deep enough to take the clips. Beyond that, the blind must clear the handle through the full tilt and full turn range, and the published guidance from blind specialists is to test exactly that before finalising the fit. A blind that hangs loose is the wrong choice here: because a tilt-and-turn sash opens inward, a free-hanging blind will swing and catch every time the window tilts.

Is an integrated blind sealed inside the glass worth it?

It is worth it when dust, cords and cleaning access are the real problems, and it is a poor trade when serviceability matters more. The deciding question is whether the unit can be opened for service. In most products sold today the blind sits inside a sealed thermal assembly, so a snapped cord or a worn tilt mechanism means replacing the insulated unit, which is a glazing job rather than a blind job. Note also that published window guidance calls for thermally toughened glass when a blind is enclosed in the unit, because the airflow path is gone.

Do I still need external shading if I have already specified solar-control glass?

Usually yes, and for a reason that surprises people: the two are not substitutes, they act at different points. Glass changes what crosses the glazing. External shading stops the energy before it gets there. Published comparisons put the difference in the region of the glass blocking roughly half of the solar gain versus external systems blocking around nine tenths, which is why guidance for highly glazed spaces keeps landing on external and mid-pane measures first.

Why does my blind rattle when the wind blows?

Because a loose-hanging blind is not captive. In framed clip-in systems the frame itself acts as the guide, so the fabric cannot swing when the sash is tilted or the wind gets up. If your blind rattles, it is either a free-hanging product being asked to do a guided product's job, or a guided product whose cord tension has gone slack.

Can the blind be added after the room is glazed?

Internal blinds, usually yes, subject to bead depth and handle clearance. Integrated blinds and external screens, effectively no: one requires a new insulated unit, the other requires structural fixings, drainage and often consents that are far cheaper to deal with before the finishes go on. If a motorised blind is on the wish list, the cable decision belongs to first fix, not to the final week.

If I want a glass sun room, what should I actually ask you for?

Ask for the section drawings with the glazing rebate dimensioned, confirmation of whether your chosen sash accepts a clip-in blind frame, the handle projection in millimetres, and the rated sash weight for your series and configuration. We can supply the drawings and confirm the construction. The rated sash weight we do not publish, and the shading supplier's fitted weight is their number, not ours. For the glazed envelope around the room, our sliding door and tilt and turn series are the relevant starting points, and you can see how they have been used in completed work on our projects page. If you want the whole envelope priced as one package, reach us through the contact page with the four measurements from the previous section attached.

Bottom Line

There is no best blind, because the word covers three positions and physics has already ranked them. External rejects the most, integrated trades repairability for cleanliness, internal manages glare and privacy and cannot reject most of the heat. Choose the position first, then the fabric.

When you get to the fabric, ask for gtot rather than a colour, ask which glazing it was measured against, and check the absorptance as well as the openness factor. On the three published fabrics we looked at, absorptance ranged from 18 percent to 39 percent, and the two that share the same three percent openness differ by a factor of about 2.2.

Then deal with the part nobody prints. Glass makers ask for clearance and free airflow at the glass surface, and one window manufacturer puts that at 50 millimetres. The flush internal blind that performs best sits against the glass. Both statements are from reputable sources, and the warranty exclusion for thermal stress means the cost of the ambiguity falls on the buyer. Get the answer in writing before you order.

If your brief is a full glass room, it helps to look at sun room designs together with the glazing schedule, because the shading positions that are cheap now are the ones that need a fixing point, a cable or a structural bracket, and all three have to exist before the room is finished.