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Ask an Expert - PVCu

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 http://www.ask-questions.com/yabbse/index.php.

Question submitted by Paul

I need to add trickle vents to my flat's woodgrain uPVC windows. Can you please suggest a supplier or manufacturer.

This question answered by the Windows Today editorial team - Just about any replacement window supplier or manufacturer should be able to supply you with "trickle vents". One "brand" we know are called "PVCu Solvents". These are manufactured by Greenwood Air Management (Part of Marly PLC) and while we doubt they sell directly to the public they may be able to put you in contact with a local supplier. They have a web site at http://www.greenwood.co.uk

Installing Trickle vents makes good sense because they protect the building fabric from damp. Trickle vents are not usually very expensive - 15 - 20 each is typical - excluding fitting.


Question submitted by Rocky

I have several questions actually. I have had quite a few different quotes and am VERY CONFUSED. Several installers seem to be using Eurocell, Selecta, Rehau, Duraflex. How do these compare to other products? I am worried about discoloration of the plastic and generally deterioration over time. Having also had more expensive companies in such as Cambrian and Everest, they have concerned me by saying if I put in cheaper windows I may as well not change them at all! Very simply, I am just looking for a good installer of a good product at a reasonable price. I live in South Wales, and if you are able to suggest a reputable company, I would be eternally grateful.

This question answered by the Windows Today editorial team - All the brands you mention are of good quality and well respected. Also today every PVCu window extruder we know gives a warranty on the colour fast issue.

While we are often asked to review individual products it is still our view - that the most important consideration is the reliability and professionalism of the individual installation companies. Many companies will offer similar or even identical products - and virtually all these products will perform satisfactorily provided they are installed correctly. Often in marketing their products companies will go to great pains to "prove" that their product is best and sometimes it can be difficult for a consumer to know whom to believe. Its for this reason we suggest you concentrate most of your buying decision on the calibre of Installation provided, the Guarantee/Warranty being offered and the likely after sales service.

Sometimes its easier to ignore the "money" side of things for a moment and then ask yourself what company you would prefer to do the work. This will often be a useful pointer in deciding who to award the work to. Its also our view that rarely will the "cheapest" price represent the best value overall when we compare long term issues such as guarantees and after sales service. This is what for us separates all these companies offering what often appear to be similar products.

Question submitted by Nigel

Is there any difference between PVCu windows fitted in a conservatory and those fitted in a house? I have had different sales people giving different responses to this question; one suggested house windows are not as strong and should not be used in a conservatory. Another said they were identical. Can you help?

This question is answered by the Conservatories Online editorial team - The "base" PVCu extrusion used in conservatory construction is often the same as that used in house windows. That said, most conservatory companies will add to the base spec with better quality reinforcing (say fully reinforced) or thicker framing.

For instance some conservatory companies will prefer to use the outer frame section usually associated with door frames for the window framing in their conservatories. (The thickness/width of outer frame in most windows is 50 - 55 mm while the thickness of the door framing is usually 70mm) A thicker frame - fully reinforced will give better structural strength. Also some companies will use more frames to assembly a conservatory than others - often joining these frames with special structural mullions. (By this we mean that some companies will manufacture each section/frame separately while others will make one larger "window" that could be divided into say three sections) Clearly these differences have considerable effects on the prices quoted and you should expect to pay more for a conservatory made up out of individual frames.

Please note that having the conservatory made out of a greater number of frames is more important with a glass roofed conservatory than say a polycarbonate roofed conservatory. (Because of the greater weight of a glass roof) While we like using a greater number of frames to construct a conservatory you should note that using more frames will also add to the "bulkiness" of your conservatory and this may not be to everybody's taste.

When attempting to compare "like with like" in quotations you receive for your conservatory you should bear in mind the above points in particular. Just because the drawings look similar and the all companies specify PVC-U with say a polycarnonate roof does not mean that the specifications are identical. For this reason we always advise people to be especially careful if they receive one price that is considerably lower than the rest of the quotes received.

Question submitted by Paul

I am thinking about purchasing a pvcu frame called PLASTMO. I cannot find this type of Extrusion mentioned in your website. Can you please advise of any problems this system may have or its good points. It also uses a 4-16-4 Glass-air-Glass double glazed unit, how much more efficient is the 4-20-4 Glass-air-Glass double glazed unit at noise reduction.

This question answered by the Windows Today editorial team - PLASTMO are a very well respected PVC-U extrusion that originally came (we think) from Denmark. They claim to be one of the first companies to concentrate on the production of products from polyvinylchloride unplasticized, now known as PVC-U - starting to produce extrusion over 30 years ago.

They now have good distribution in the UK and Ireland and offer two depths of extrusion - 62 mm and 70 mm. We suspect that you have been offered the 62 mm extrusion as the sealed unit indicated is 24 mm over all (4-16-4). Generally speaking 28 mm units (4-20-4) are more common in 70 mm extrusions. While a 20 mm air gap does offer slightly better sound insulation - the difference compared to 16 mm air gap is very little.

All Plastmo windows feature advanced triple chamber construction, which entirely isolates the frame's steel reinforcements, ensuring that moisture cannot seep in. The steel reinforcements are also galvanised to ensure they don't deteriorate. All the usual features such as espagnolette and shoot bolt locking are available.

As we often say within our web pages - the qualities of window and door frame being offered by most PVC-U systems companies are generally very good. The more important thing to concentrate on is the quality of the local installer. It's them and their service which will ultimately determine your satisfaction.

Plastmo have a very attractive web site at http://www.plastmo-style.co.uk/

Question submitted by Andrew

We have a 75 year old house, with original sash windows. We'd like the benefits of pvc-u double glazing, whilst preserving the overall appearance of the house. I've seen many installations in houses like ours, and remain to be convinced by most of them. Does anybody make pvc-u double glazed sashes ? Are there any other options ? The windows need replacing, so secondary glazing doesn't seem to be sensible - it doesn't look too nice inside, either !

This question answered by the Windows Today editorial team - Sliding sash style PVC-U windows are available. One extruder with a good reputation for this type of window is REHAU. There are many fabricators and installers of the Rehau product and it should not be very difficult to find a supplier who can supply you. Many companies advertise Rehau in their adverts but if you have any problems you could contact Rehau themselves. Their web address is 
They have an article on their range sliding sash windows (called the Heritage vertical sliders) - click here for link - In this particular instance PVC-U sliding sash windows were used in a conservation area. This is quite an achievement for a PVC-U product as until now PVC-U has rarely been used in conservation areas.

Question submitted by Alister

What is the difference between u-pvc and pvc-u, one supplier claims better aging, particularly colour, for pvc-u.

This question answered by Peter Taylor of Zenith Windows - To answer the question very simply, there is no difference between u-pvc and pvc-u. Both terms refer to unplasticised (hard) pvc which is used extensively in building products where rigidity is an important attribute.

Plasticised (soft) pvc on the other hand is used where flexibility is important, for example medical tubing applications, insulation sheathing on electrical wiring, etc. Pvc-u is more to do with commonality of terminology world-wide than it is to do with formulation. Any claims of better performance of pvc-u over u-pvc are therefore spurious.

The Zenith Windows web site is found at http://www.zenithwindows.co.uk/

Question submitted by Anne

One of the companies that have quoted for upvc double glazing has stated their units are fully reinforced with wood. We have not come across this before as most others are reinforced with galvanised steel. Is wood a good reinforcement option?

This question answered by the Windows Today editorial team - A few companies do use wood to reinforce. In our opinion it is a perfectly good reinforcing material. We suggest you make sure the extrusion is of a good depth (60 mm and above is OK) and manufactured to a high standard.

You may also like to note that we know of several companies who always use wood to reinforce the PVCu frames of their doors - as they claim this makes for a more 'rigid' and secure door.

Question submitted by Alan

Many firms are not very clear on what UPVC system they use but others claim to use "high quality" sections with names such as Kommerling, Rehau and WHS Halo. How do you judge the quality of a system? Which, in your opinion, are the leading contenders?

This question answered by the Windows Today editorial team - All of the companies you mention above are leading contenders - offering good quality PVCu extrusions. We suggest you examine the thickness of frame (depth from inside to outside). Generally speaking a 60-mm thickness is the lowest you should except. Go for 65 mm and 70-mm thickness if available. Also enquire about the thickness of the PVCu walling in the extrusion. The extrusion is a multi-walled section (not solid) and wall thickness of 3 - 3.5 mm is normal.

The types of glass used will also have an effect on the overall quality and performance of the window. Pilkington K Glass (for better insulation) is worth considering.

The other issue to consider is security. There are many different types of lock etc on the market and most are not supplied by the extruder but by other hardware suppliers. Check with your supplier the security features of their window and make your final decision based on this. Remember its possible to have two suppliers supplying exactly the same extrusion - for instance the REHAU extrusion - but with entirely different locking features. To compare "like with like" is a lot more complicated than saying both suppliers use the same extrusion.

Question submitted by Alan

How do you see the advantages and disadvantages of PVCu and aluminium for replacement windows?

This question answered by the Windows Today editorial team - PVCu offers the following advantages...

* Good insulator
* Low maintenance
* Many suppliers / usually the cheapest option today
* Now available in wood grain and coloured finishes.
If it has a disadvantage it maybe that it has relatively low structural
integrity. This is overcome with steel or aluminium reinforcement. Also it
can be susceptible especially in south facing situations to "expansion" in
sunlight. Again using "fully reinforced" frames can reduce this.

Aluminium offers the following advantages...

* Virtually no maintenance over its long lifetime
* Slim, strong sections that will not warp or twist
* About one third the expansion of PVC-u
Its main disadvantage is that it's a relatively poor insulator. (However
thermal break aluminium frames are available which offer better insulation)
It is also usually more expensive than PVCu

Question submitted by Steve

We have had 3 quotes, all of which were very similar. However each quote was for a different system. The 3 are Rehau, Profile 22 & we think Synseal. What is the difference between them and which would you recommend? 

This Question answered by Tina Dunlop @ Almost Impartial Guide - The three PVCu Systems you mention are some of the most respected extruders in the UK today. My personal opinion - based on looks - is a preference for the REHAU system. If you go with this then ask for their 70mm extrusion. (They also do a 60 mm extrusion). Profile 22 also has good looks - but its not a system I have had a lot of personal experience with. Synseal have several sizes of extrusions. I would only consider their SHIELD system which like the Rehau extrusion is available in 70 mm sections. In terms of cost I would expect the Rehau extrusion quote to be slightly more expensive. I would also opt for the internally beaded option if available. Finally - I think you would be happy with any of these extrusions. The more important thing is the quality of Fit. That will determine your ultimate satisfaction. Make your final decision based on the quality of the company and evidence of previously completed work. 

Question submitted by Lisa

We are interested in a blue conservatory, please can you tell me if there is a stockist for coloured PVCu or aluminium? 

This Question answered by Tina Dunlop @ Almost Impartial Guide - Coloured PVCu has started to become more popular. At present however only a fairly small number of companies supply it. It will be a little more difficult to locate coloured options for domestic use. I suggest you contact an aluminium window supplier and ask if they could supply. Most can - but I would think it's likely to be expensive. 

Question submitted by Lucia

I am a bit confused about the different type of frames available on the market. Whereas hardwood is pretty self-explanatory, aluminium and PVCu are more confusing. For example, we have seen frames, which are aluminium on the outside and PVCu on the inside. The salesman says they are good in terms of insulation and the inside does not get too cold, thus making it less susceptible to condensation but in your web site and other brochures we have seen always give the option of either aluminium or PVCu. Can you clarify this point please.

This Question answered by Tina Dunlop @ Almost Impartial Guide - About 10 - 15 years ago the "thermal clad" option - combining both aluminium and PVCu was quite popular. Today only a few companies still do it. The reasons for this are most likely both "political" and "economic" in that most Aluminium Extruders didn't particularly want to promote PVCu as an alternative (preferring to promote a thermal break option) and PVCu extruders did not particularly want to promote Aluminium. Speaking personally "thermal clad" aluminium framing would not be my preferred option. This does not mean you should not consider it - especially if you like its looks. It's a perfectly good option to consider along with PVCu, Hardwood and Aluminium. Like all the material options - it's a matter of personal choice. It might also be worth remembering that quite a number of the conservatory roofing systems use a thermal clad system for the roof rafters - i.e. Aluminium Roof Rafters - Clad in PVCu - so at least in terms of roofing it is not unusual. What really matters is finding a reputable supplier and installer who can do "justice" to whatever material is used. Your experience is quite unusual in that you have come across this product. As you say few brochures and this web site did not even mention it as an alternative. At least your question has corrected that omission on this web site. Thank You. 

Question submitted by Cathy

Please tell me what the best PVC product is i.e. should it be reinforced with steel or aluminium? Any tips would be helpful.

This Question answered by Tina Dunlop @ Almost Impartial Guide - In my opinion - there is really not much to choose between Galvanised Steel Reinforcement or Aluminium Reinforcement. Both do the job and leading companies uses both alternatives. What I do find is that "salespeople" will often make exaggerated claims one way or the other in an attempt to sell their product. Typically the arguments go as follows - Steel is stronger - but more likely to rust if the galvanisation is removed and Aluminium is not quite so strong - but will not rust! (That's the simplified arguments!)

As an example of the "exaggeration" that can go on - I have know of companies to show photos of windows with rust coming from them! What is not explained is that when screws are inserted into galvanised steel is that a small amount of "swarf" is removed and with that the galvanisation. It's possible for the swarf - which will always drop down to the bottom of the frame to "rust". The evidence of this quickly disappears as the swarf oxidises. This rusting is "not catching" and will not pass to the rest of the reinforcing.

Sorry if my answer is not "conclusive" - but I feel the more important consideration is the overall calibre of the company you chose and the quality/looks of the PVCu system - not whether Steel or Aluminium is used for reinforcement. The only other question I would raise with a supplier is "if the frames are fully reinforced"? - In my opinion they should be. Some suppliers will use terms such as "reinforced where necessary" - this is clearly not the same as "fully reinforced".

Question submitted by Andy

Some say their Brown/White PVC combination is "OK" because the brown finish is only a film on white PVC. Obviously the physics of this is dubious as it is the colour of the finish that determines the radiant absorption, not the internal material (at least I would have thought), but the thought arises - how durable will a surface finish be if it is only a film?

This Question answered by Tina Dunlop @ Almost Impartial Guide - The physics are indeed dubious. The other issue is that if the material ever gets scratched - you will see the "white" underneath. (Scratching is hard to do - but possible) Additionally suppliers cannot clean the surplus from the welded PVCu corners in the same way as they can with white PVCu. This means that the area around the weld has to be left slightly "raised" as mechanically cleaning the corners (as would be done in white PVCu) would mean the white PVCu underneath would show through.

Question submitted by George

I have heard that using mahogany PVCu in conservatories is not as durable as the white. Is this true? 

This Question answered by Tina Dunlop @ Almost Impartial Guide - It is true to say that within the "trade" you will find people/companies who do not like using Woodgrain style PVCu for conservatories. The main "gripe" is that woodgrain style conservatories tend to "expand" more when subjected to direct sunlight. This causes "sticking" on doors etc. (When we are out in the sun most of us wear light coloured clothing as this is cooler.) Having said that, a large number of companies including some of the most reputable do supply woodgrain style conservatories. Personally speaking (and that's all I can do!) I would not have too much trouble using woodgrain for a conservatory - provided it's a complete woodgrain option - i.e. woodgrain inside and out and ideally not south facing. Make sure your supplier provides their frames "fully reinforced" - this will help reduce "expansion". Also it's a good idea to use heavy duty/flag style hinges on the doors. What I would not recommend is woodgrain on top of white PVCu - with this option you would have woodgrain outside and white inside. This is not a good option due to varying expansion rates etc. (This is, of course, only my opinion!) 


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