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Conservatories, Sunrooms - Your questions Answered
Polycarbonate (13)

Please note: Most of the answers we feature here are from 1999 - early 2002. We endeavour to keep all links etc up to date, however if you spot any errors please let our webmaster know at It should also be noted that some replies may change in light of changes to legislation especially with regards to Planning Permission and Building Regulations. To submit a new question or to query an existing question visit

Question submitted by Karen

A small conservatory firm tell me that they use 35mm polycarbonate roofing as the 'u' value is 1.36 per m2 at 0 C, whereas 25mm has a value of 3.6 per m2 at 0C. From what I've read on your site this second value is wrong. Can you please advise? The heat retaining properties of the conservatory are very important as we have a site facing due north. We want to have a lean to design, 6.9 by 2.4 approx. to use as a year round room.

This question is answered by the Conservatories Online editorial team 35 mm polycarbonate is starting to become more widely available and the usual "u" value quoted is 1.4W sqm K - a very good level of insulation. The 1.36 figure quoted by your suppliers may well be correct - but the figure quoted for 25 mm is wrong. No doubt this is a genuine mistake - we find a lot of confusion over "U " values. A typical "U" value for 25 mm polycarbonate is 1.6W sqm K (The lower the "U" value - the better the insulation)

Until recently in had not been easy to find a roof system (rafters etc) capable of accommodating 35 mm polycarbonate. A number of systems have now become available and one of the first was a special "LOW PITCH" roofing system for lean-to style conservatories produced by Quantal Conservatory Roof Systems.

We suspect your supplier may be using the Quantal system. If a high level of insulation is a priority then having 35 mm polycarbonate in your specification is about as good as you can currently get.

The Quantal web site may be found at

Question submitted by Ashley

What are the main factors to consider when deciding between bronze and clear polycarbonate? One installer told us that clear polycarbonate quickly becomes covered in green slime if used on north facing conservatories. Another installer said this was rubbish and that light throughput was the only issue.

This question is answered by the Conservatories Online editorial team - All conservatory roofs need cleaning occasionally. (For most people twice a year) Provided this is done there should be no significant build up of "green slime" as you describe it. We guess it could be possible that any build up of dirt etc would be more visible on clear polycarbonate - but that doesn't mean that other types of polycarbonate don't also need cleaning.

It is true that different shades of polycarbonate will let varying amounts of "light" in and clear will off course let in the most light. It should be noted that "clear" polycarbonate is not "clear" in the way that glass is. It is fairly "opaque" in our opinion. Also you should know that on North facing conservatories "bronze" tinted polycarbonate will cut out more light - both to the conservatory and any room it might be attached to. While by no means a rule we would suggest that bronze tinted polycarbonate is most appropriate on South and West facing elevations.

Question submitted by Karen

Oh how I wish I had found you before we had the conservatory built!!! The usual problem I'm afraid. Too cold to use after September even though we have a rad in there linked to the house central heating. I have toyed with the idea of roof blinds to help conserve heat loss but the cost is prohibitive to say the least. Recently I discovered a company who provide "solar inserts" and I have spoken to a user of these who says they help keep heat and glare to a minimum in Summer but I fear this system will not help us with insulation. The cost will still be over 1,000 Can you advise if you know of this product. Is it possible to have the present polycarbonate roof replaced with a thicker one or even a double glazed glass one Help we are desperate to use our conservatory as we love it!!!!!

This question answered by Tina Dunlop - There are several companies who offer solar inserts. One company we know of is INSU. They have a web site at They claim to be the suppliers of the "original" solar inserts.

We should say that we have no experience ourselves of using this product - but do know the INSU company quite well. They seem very sincere and genuine to us. They claim that INSU products (which consists of products in addition to the solar inserts) will exclude up to 80% of summer heat and cut glare while reducing winter heat loss by up to 70%. That sounds remarkable to us. The only criticism we can think of is that these products will quite likely also reduce the amount of light that enters your conservatory. This is not we think controllable in the same way that you can control blinds.

Question submitted by Brian

We are getting confusing signals from people quoting for a conservatory. In relation to the roof, some vendors are saying that polycarbonate is better for a lot of reasons and others say that it darkens the inner room / it looks cheap and also that the noise level during heavy rain can be very annoying. Can you please advise of your experience on this. Also is the standard for polycarbonate 16mm or 25mm. The conservatory will be south-west facing. (question edited)

This question answered by Tina Dunlop - Each roof product has its advantages and perhaps disadvantages depending on what you are looking for.

16 mm polycarbonate is still the most popular alternative - however 25 mm polycarbonate is growing in use - mainly because of its good levels of insulation. 25 mm polycarbonate is a little more expensive but in our opinion it is worth it.

We don't think that polycarbonate looks "cheap" especially if its fitted properly using a good roofing system. If polycarbonate is fitted badly without the correct roof pitch and without proper finishing profiles such as "sheet end closers" it can look bad. Look out for conservatory companies using quality roof systems from companies such as Ultraframe and Quantal - polycarbonate looks good in theses systems.

No matter what roof material (polycarbonate, glass, slate or tile) you use there will be some noise from the rain internally, as these structures do not have any ceiling in them. Its true that 16 mm polycarbonate in particular can be quite noisy in the rain - but then again it's a matter of personal preference. (We have even known people who like the noise of the rain on the roof and will deliberately sit in a conservatory when it rains!)

Its also true that no matter what roof material you use that a certain amount of light will be taken away from the room its attached to. (This is even true with glass roofs, as you will almost certainly fit blinds in a glass roof). We think its a good idea wherever possible to have additional natural light sources in a room - perhaps from a side window that the conservatory does not cover over. In a South West facing room such as yours we do not feel this would be a major problem.

Question submitted by Dave

My conservatory builder has had to replace a faulty polycarbonate roof panel. However, where all the other panels have cells that are 2.5cm wide, he has tried to replace the faulty panel with a panel with cells 2cm wide. When challenged on this he claims that his supplier cannot remember who they sourced the original panels from, and that they are having trouble locating our specification of panel. Is it really that difficult to find somebody that could supply the right panels?
This question is answered by the Conservatories Online editorial team - It may be hard to believe but we do hear of your type of problem quite often. Its not uncommon for suppliers of conservatory roofs to have more than one polycarbonate supplier and to also change between suppliers quite often. That said we do think it reasonable for you to expect replacements to be on a "like for like basis" in all but the most exceptional situations. Even if the identical match cannot be found - a match quite close to the original should be possible. Your supplier has clearly been quite responsible. (i.e. they have at least attempted to correct the situation) However we do feel that the supplier or their supplier could if they really wished find out whom originally supplied. The specification may no longer be available (its more common to find cells 2 cm apart) but we do feel that before giving up a better explanation is required.

It may also be worth your while taking a sample of the original polycarbonate around local stockists and seeing if they "recognise" it.

You don't say it in your question but we do sometimes find that suppliers will having varying "degrees" of tint in their bronze or opal tinted options. This can also lead to problems if a replacement becomes necessary later. A tip we give to all buyers is to save any suppliers records you may find with your new conservatory such as the company who manufactured the frames or roof. Additionally items such as polycarbonate will usually have a protective film over it, which will indicate the polycarbonate manufacturer. Leading names include Polygal, Macrolon and Rohm.

Question submitted by Peter

One company we are dealing with specialises in Solar strips for Polycarbonate roofs. Do you have an opinion of this product? (Question edited).

This question answered by Tina Dunlop - For help with answering this question we consulted David Anderson of INSU - UK - one of the UK's leading supplier of Solar Inserts. While David can hardly be described as "impartial" I do feel he has some valid points to make.

1.Technical Performance.

When a solar strip or tape is used it must be inserted into the roof by roding which means that the strip lies on top of the centre horizontal portion of the cavity. This limits the performance of the product, and may compromise the integrity of some roofs. The reason for this is that strip material absorbs up to 35% of the sun's heat, which leads to an increase in the temperatures inside the roof.

For this reason INSU solar heat reflectors are shaped like a staple to ensure that any absorbed energy is transmitted directly to the outside surface of the roof and hence to the cold outside air. (They are not rodded into the polycarbonate)

This heating up of the internal part of the roof leads to a certain amount of heat entering the conservatory, which limits the performance of the product. This would not in itself be sufficient to cause a loss of comfort in a high roof conservatory, say average height of 9 feet or above, but below this there may be insufficient solar heat rejection performance especially on lean too types, particularly those fitted onto bungalows.


With some roofing systems and polycarbonate, there could be difficulties with guarantees. The reason is that PVC is a thermoplastic material, which softens with increased temperature. The danger is that this could lead to shrinkage of the lower roof panel and loss of integrity of the roof.

Because strip type products have no inherent rigidity and are simply tapes they must be rodded up the roof, there is also a danger of the rod puncturing the top cavity seal. It is difficult for an operator to feel the thin piece of aluminium tape, which forms the top seal. This is why conservatory companies supplying Polycarbonate roofs may void the supplier's guarantee by fitting this type of product.

Some time ago INSU - UK tried this type of system but because of the above limitations then decided to develop the Solar Insert heat reflector system (in a staple shape) instead.

The INSU web site is at

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Question submitted by Richard

My builder quoted me on my new Conservatory for a Venetian Polycarbonate Roof. He has now had problems with the delivery of this product and has advised me that a Bronzed Polycarbonate roof will do just as well. The reason for choosing the Venetian roof was to help filter the UV rays out, and in turn cool down the conservatory. He says that both types of roof will be the same heat wise. Can you clarify? Also, would there be a difference in pricing on these two products? Many thanks!

This question answered by Tina Dunlop - I am aware of some difficulties in obtaining this product. However I do believe its still available if you "hunt" around. One company that did sell this product was: Formerton Sheet Sales Limited - Tel 023 8033 2761 I think that the Venetian alternative is both attractive and very good at reducing heat build up - certainly better than bronze tinted.

By the way "Venetian" is one brand name for a polycarbonate with opaque striped pattern, screen-printed on one side. It is well suited for many glazed spaces where there is a need to reduce the effects of solar gain. I think some companies have experienced problems with the screen printing coming of whenever the protective film covering the polycarbonate is removed. Apparently this is not really much of a problem if the protective film is removed slowly - rather than "ripped" off quickly as is the inclination of most conservatory installers!

The venetian alternative is more expensive than bronze tinted polycarbonate - but not by a great deal. I would expect a small reduction if you went with bronze tinted. (Typically 200 on a 4m x 3m conservatory)

Question submitted by Chris

I have had two companies quote to supply and build a new conservatory, one has recommended a polycarbonate roof and the other a material called "everlight" as part of a self-supporting roof system. Have you heard of Everlite and if so is it any good?

This question answered by Tina Dunlop - I am familiar with Everlite which is supplied to the "trade" the UK by a company called Plastmo. (Tel 01604 790780) This product is popular with the DIY market and many small builders as it comes ready-packed in a kit form. It is mainly used for leanto installations. In my opinion it is a "perfectly good" roofing material although given the choice I would personally choose 25 mm polycarbonate. I suggest you get a sample of this roofing material and compare with polycarbonate before making a choice. It really is a matter of personal "taste".


Question submitted by Keith

I have a conservatory which I would like to renovate. It currently has a polycarbonate roof which I would Ideally like to replace with Glass. However, I suspect this would be expensive and not something I could do myself. Is there any alternative plastic product to polycarbonate which would give a transparency more like glass?

This Question answered by Tina Dunlop - Yes, glass may prove expensive. Also as your original roof was polycarbonate, the support structure may not be strong enough for glass. However, yes there is an alternative plastics solution with the clarity you are seeking - A twin-wall acrylic called PLEXIGLAS ALLTOP SDP. This sheet has excellent clarity with 91% light transmission. Special 'NO DROP' coatings ensure that the clarity is maintained by making the sheet readily washed down by the rain and dispersing any interior condensation. Acrylic sheet withstands long-term weathering very well, having excellent UV resistance. This product has good impact resistance and offers excellent sound reduction properties.

One other "advantage" that is claimed for PLEXIGLAS is that it will be less noisy than polycarbonate in the rain etc. This is a issue that I find more and more people are considering. (This is mainly because they are extruded with thicker walls, as evidenced by the much higher weight per square metre.)

For more information, prices, etc please contact your nearest branch of Amari Plastics, or their specialist building products unit on tel no. 0115 928 6550.

They have a Web Site at - however there is not a lot of information on PLEXIGLAS there.

My grateful thanks to Clive Husselbury at Amari Plastics for his considerable assistance in answering this question.

Question submitted by Jon

We have a bathroom which is an extension to the house measuring roughly 4m x2m with a traditional sloping roof tiled with slates. I'd like to lighten the space and have considered adding a skylight/velux window etc. Now I'm considering "glazing" it completely with polycarbonate sheeting. I've not seen this sort of renovation advertised before but it seems like an excellent and cheap alternative to traditional roof windows etc. Is this, in your opinion, a practical and viable option?

This Question answered by Tina Dunlop - As your bathroom is part of your main home - changes such as this should in "theory" be subject to building regulation approval. It's unlikely that could be obtained if you use some thing like 16 mm polycarbonate. 

Another possibility would be to use double glazed units in your roof - incorporating Pilkington K Glass and Argon filled. This would "satisfy" the insulation requirements of Building Regulations and would in my opinion be very attractive. (Not particularly cheap!)

25 mm polycarbonate would give similar insulation to Pilkington K Glass - however even the "clear" versions are quite opaque and may not give the effect you envisaged.

Question submitted by Vic

I have a 20mm clear polycarbonate roof, which is almost totally filled with condensation. It looks unsightly and will probably turn black in due course. The vendor has replaced the panels, but the condensation returns immediately. Is there anything that I can do?

This Question answered by Tina Dunlop - It is very unusual for polycarbonate to condense in this way. The usual practice when cutting/glazing polycarbonate is to "tape over" the exposed ends with either a glazing tape or more often a "breather" tape. With a "breather" tape you are still sealing the ends of but at the same time allowing the polycarbonate to "breath" via a gauze in the tape. Additionally the polycarbonate should be capped of at the eaves end by means of a "sheet end closer" profile - manufactured in either PVC or Aluminium. The above is pretty well standard instructions from the polycarbonate suppliers and provided it is adhered to you should have no problems.

It may be worth checking if your vendors carried out these processes.

Another suggestion from me on polycarbonate is - never glaze a roof on a wet/damp day. If you do then you have more chance of trapping moisture inside the polycarbonate - resulting in condensation. Additionally you should check that your conservatory roof has adequate fall/slope. (As a minimum I would look for a roof slope of eight degrees).

You may also find that if the conservatory is heated better - then condensation inside the polycarbonate is less likely.

Question submitted by David

I would be grateful for your advice. I wish to upgrade my existing conservatory by changing the roofing material. What "shade" of polycarbonate do your recommend in the conservatory roof? I think I would prefer an opaque roof. Glare can be handled with blinds etc. What can be done to keep temperatures down? Ventilation? Thank you.

This Question answered by Tina Dunlop - The best way to evaluate polycarbonte's is to hold small samples of it in your hand and "look" at the sun through them. Clear, bronze tinted and opal are the most popular choices. Your supplier should be able to provide some small hand samples.

Clear will give the least protection from the sun and may not be the best choice in a south-facing situation. However if you where north facing and concerned about reducing the amount of light entering the room your conservatory is attached to then this may be the one for you.

The bronze tinted version is generally speaking considered the most attractive option although I would say glare - especially in south facing situations can be a problem.

Opal tinted polycarbonate probably offers the most protection from glare but you could also consider using slightly newer products such as "bronze/opal" combination polycarbonate (bronze tint outside and opal inside) or "Ultra shade" (polycarbonate which has been screen printed one side in order to filter out the glare). The bronze/opal combination is particularly good at reducing both heat build up and glare.

With regards to ventilation I'm assuming there are only a limited number of openings in your conservatory at present and it's not possible to add in any additional openers. One way around this is to fit opening roof vents. These are quite easy to fit and fit directly into polycarbonate. Another way is to fit a "solar powered" extraction fan in the roof polycarbonate which is powered by the sun. These items are available from conservatory suppliers or you could try a retailer of polycarbonate supplies. You may also like to consider adding a fan internally.

Question submitted by J Chard

My conservatory supplier says that if I have 25mm polycarbonate roofing instead of 16mm it will be noisier when it rains as being thicker it creates a drum like effect. do you agree? They also say I will not need Pilkington K glass. I see that a lot of suppliers say it is not needed, as it will be too hot in the summer. How do I know Pilkington are telling the truth when they say it won't be too hot?

This Question answered by Tina Dunlop - I have never heard of 25 mm polycarbonate being noisier than 16 mm polycarbonate. Polycarbonate is generally noisier than glass roofs - but if any thing I would have thought 25 mm would have been less noisy than 16 mm due to the extra sound insulation afforded by the thicker material. I really don't think there can be that much in it.

I do think you need to ask yourself why your supplier is so determined to sell you "solutions" which clearly are less efficient and of less practical benefit in the long term. I have answered questions on Pilkington K glass previously and all I will say here is that if you want an all year round conservatory then low E or K glass is virtually a must. If you compare the experiences of owners with normal double glazing and 16 mm polycarbonate with those who have K glass and either glass roofs or 25 mm polycarbonate installed then generally you will find that those with the higher specs., report the most satisfactory results. (Less condensation or damp with better heat retention in the winter months / evenings.) Owners / Users of conservatories are the real test. There are still a few companies who for whatever reason are reluctant to offer these higher options. Their motivation is not clear to me. I believe in consumer choice - you should at least be offered the extra options - if you don't take them up because of reason of cost or what-ever, then so be it.

One final thought - If it was true (which it is not) that K glass makes your conservatory excessively hot in the summer months - which would you prefer? A conservatory streaming in condensation during the winter, requiring constant heating which "disappears" out the window? Or perhaps an overly warm conservatory during the summer when you at least have the option of opening the doors or windows?


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