Expanding Foam for Glazing.

[paro]

Hi All - I have someone installing the glazing for me at the moment (I was on the fence about doing it myself and thought it better to get some kind of warranty). Is a lot of expanding foam around the whole frame the norm nowadays? There are some pretty heafty gaps of 20-30mm in places which seems a lot. I appreciate that it helps with cold bridging but it seems to be the only thing other than the timber cladding I'll be installing that will be holding back the weather. I had kind of anticipated some kind of trim that was sealed to the block with mastic or just something else. I've used foam for other external bodges around the house until I get to it later but after a while they start to look weathered and like it wouldn't hold up long term. Maybe just a newb worry over nothing. 

 

Could anyone point me to a reference guide on what is right / wrong for installing doors and windows?

 

Thanks, Paul

[Mr Punter]

You are right.  Foam is not suitable for long term exposure.  It needs to be covered with some trim, like plastic, timber, metal etc or rendered.  Also, most foam is not closed cell and will let water through.

[SBMS]

7 minutes ago, paro said:

Hi All - I have someone installing the glazing for me at the moment (I was on the fence about doing it myself and thought it better to get some kind of warranty). Is a lot of expanding foam around the whole frame the norm nowadays? There are some pretty heafty gaps of 20-30mm in places which seems a lot. I appreciate that it helps with cold bridging but it seems to be the only thing other than the timber cladding I'll be installing that will be holding back the weather. I had kind of anticipated some kind of trim that was sealed to the block with mastic or just something else. I've used foam for other external bodges around the house until I get to it later but after a while they start to look weathered and like it wouldn't hold up long term. Maybe just a newb worry over nothing. 

 

Could anyone point me to a reference guide on what is right / wrong for installing doors and windows?

 

Thanks, Paul

30mm is too much. You could put trim on and foam behind it. 

[paro]

Thanks. I'll definitely do the trim thing then.

[Nickfromwales]

4 hours ago, paro said:

Thanks. I'll definitely do the trim thing then.

You mean you'll ask them to do it as 'makeup' ? They should finish this so your external finishes go up to their makeup, if being left exposed for any length of time.

[paro]

Well I want to take the view that the cladding that I'll be adding is purely an asthetic facade and in no way is intended to replace the weatherproof finish that I am expecting them to leave in place. So basically if I never added the cladding the frames would remain weathertight indefintely against the blockwork. I've been reading through the FENSA guide and found te below.

 

..."A suitable backing material such as closed cell foam or PU foam should be used in the gap between
the window and wall to ensure the external sealant is set to the correct depth and will therefore adhere
to the frame and aperture (but not the backing foam) when applied. Suitable external sealant should be
applied to cover and form a water resistant joint between the frame and wall"...

 

I hadn't given this much thought, tbh, I'd assumed that by paying for a professional install it would be done right. I should have learnt this lesson by now. 

 

[craig]

On 07/08/2025 at 08:13, paro said:

I've been reading through the FENSA guide and found te below.

 

Fensa is irrelevant for a new build, you should refer to the GGF guidelines and also look at what was and what wasn't included within the installation. Unfortunately, not every installer and or supplier understands that PU foam installation only is not a suitable method. There should be a waterproof breathable membrane and or a compriband finish, then PU foam up to the that. This is asking for problems further down the line.

Edited Wednesday at 23:06 by craig

[paro]

So they agreed to provide a better finish for everything which they have now done (pics below).

 

However, -- and I didn't realise they had changed it until the last day of fitting -- because my retaining wall is in the way of the doors opening at the original position they moved the whole frame and cill further back into the aperture. The result of this is that the cill and drainage slot no longer projects beyond the outer leaf.

 

From what I am told the only water that will exit through this cill drip is what gets inside the frame through the gaskets which should be very little. I am planning a weathered threshold so the entire cill will be completely covered anyway with an aco slot drain. That said I was still expecting the drainage from the cill to have to go beyond the wall.

 

The company have told they really don't think its an issue, that the frame is sealed and there is a dpm on the inside. I am not sure that is really the point, I don't think I want any water getting in at all if it can be helped. It just feels like building in a flaw. The BI had no interest whatsoever and I am struggling to find something to push back at them to say it has to be done or not.  They had a surveyor come out to measure so I would argue this is on them and they should have proposed a wider cill or more smaller doors. 

 

If anyone has a view on why this is or isn't acceptable I would appreciate it. 

 

Thanks, Paul

 

 

[Nickfromwales]

I think it’s a zero issue tbh. What water, if any amount, that gets in there will just drop into the cavity and find its way south.

 

Good to see they came to put this right, as some just won’t. 

[Spinny]

I think with all things it can help to keep your eye on what is being done as it is occurring. Always difficult as few of us appreciate having people 'standing over us' while we do something. Even then it is easy to forget or miss things, but so much easier to adjust or correct work in progress than to get it corrected afterwards. I have probably become too obsessed with trying to work details out before the work takes place - and even then things can go awry - it sends you a bit loopy in the end.

 

I would go around and check all the doors and windows at this stage - are they plumb, positioned ok in the aperture, matching heights around the rooms, compatible with your planned finished floor levels inside and out, will open properly and with relevant clearances. And then think long and hard about any issues you find because now is the time to get it corrected even if that means having to pay for the change/correction. I had to get one window cill changed because it blocked the opening of an adjacent window.

 

(I have one door that opens against a wall and wanted it to open 90deg with clearance for the handle. Looks like it is going to be really tight now once plastered and may not open 90. Had I spotted it at the time I could have got the fitters to put it tight up against one side of the opening to give a few mm more clearance. Also had to buy and use a water level to prove that the fitters laser level was wrong and their measurements at fit were in disagreement with their measurements at survey. (Water levels actually rather useful for checking levels between inside and outside of buildings and around corners etc.)

 

PS I think doors and windows are normally sized to be about 6mm all round smaller than the opening. 

 

Edited 1 hour ago by Spinny