Air Tightness Detail on Windows

[richo106]

Hi All

 

Once again I am after some advice from BH, this time it is on how to best to install the window reveals with air tightness in mind

 

All external walls will be parge coated and I have the split tape and brick/block adhesive

 

I have 2 different scenarios, I have attached both pictures and ideally need advice on both if possible

 

On window no.1 the cavity (above and below) is going to be filled with sprayed EPS beads, I also need to install 50mm PIR backed plasterboard on that wall ideally

 

Window no.2 - the cavity is filled with PIR (thermaclass 21) and as you can see has cavity closers

 

Any advice and ideas would be very helpful as I have not done this kind of detailing on windows before (normally just dot/dabbed the reveals in)

 

Many Thanks

[Adsibob]

On window 2, I believe you tape the window to the 4 edges of the reveal, which will include taping it to the closers, using a thick airtight tape (probably at least 50mm wide, so there is 30mm on the reveal, and 20mm on the window. Then separate bit of tape to seal junction between cavity closer and inside skin wall. Then plasterboard goes on the left and right reveals, and the top reveal, whereas window sill board goes on the bottom.

 

 Window 1 should be simpler, as no cavity closers to seal.

[Chanmenie]

You could use Illbruck sp925 or Pro Clima Aerosana Visconn Fibre, both can be brush applied, then you could seal the window to the cavity closer and the cavity closer to the blockwork. Would work out cheaper than tapes I think 

[nod]

2 hours ago, richo106 said:

Hi All

 

Once again I am after some advice from BH, this time it is on how to best to install the window reveals with air tightness in mind

 

All external walls will be parge coated and I have the split tape and brick/block adhesive

 

I have 2 different scenarios, I have attached both pictures and ideally need advice on both if possible

 

On window no.1 the cavity (above and below) is going to be filled with sprayed EPS beads, I also need to install 50mm PIR backed plasterboard on that wall ideally

 

Window no.2 - the cavity is filled with PIR (thermaclass 21) and as you can see has cavity closers

 

Any advice and ideas would be very helpful as I have not done this kind of detailing on windows before (normally just dot/dabbed the reveals in)

 

Many Thanks

Save your money on Parge coat 

and spend it sealing around the door and window openings It’s also worth applying acoustic sealer around every edge of plasterboard that meets external brick or block 

I assume that your dry lining Give the fixers a bit more money to take care that all the edges are sealed By putting a Parge coat on You’ve already accepted that air will leak behind the plasterboard 

 

Parge is a diy thing 

Even the housing associations have given up on it 

 

The last Parge I applied for airtightness was for a self builder and the one before that also 

[richo106]

2 hours ago, nod said:

Save your money on Parge coat 

and spend it sealing around the door and window openings It’s also worth applying acoustic sealer around every edge of plasterboard that meets external brick or block 

I assume that your dry lining Give the fixers a bit more money to take care that all the edges are sealed By putting a Parge coat on You’ve already accepted that air will leak behind the plasterboard 

 

Parge is a diy thing 

Even the housing associations have given up on it 

 

The last Parge I applied for airtightness was for a self builder and the one before that also 

Thanks for your reply @nod  The only reason i was going to parge is because some walls will be battened and screwed. I will be doing the plasterboarding so will take extra care anyway.

 

I am guessing I can't dab onto the cavity closer so how would I do my plasterboard reveals? J Bead? https://www.gyproc.ie/products-systems/products/gyproc-drywall-metal-edge-bead - A chap at work ( I work for British Gypsum) said they have screwed the J beads into the windows and then slot the board in and dab in the inside course? I am not sure how i feel about this...

 

 

[richo106]

4 hours ago, Adsibob said:

On window 2, I believe you tape the window to the 4 edges of the reveal, which will include taping it to the closers, using a thick airtight tape (probably at least 50mm wide, so there is 30mm on the reveal, and 20mm on the window. Then separate bit of tape to seal junction between cavity closer and inside skin wall. Then plasterboard goes on the left and right reveals, and the top reveal, whereas window sill board goes on the bottom.

 

 Window 1 should be simpler, as no cavity closers to seal.

The tape I have is 80mm, i think its 30/50mm split off the top of my head

 

I don't think window 1 is very clear..there is no cavity closers on the bottom or top of this window (in hindsight there should of been!)

 

So I am not sure what to now regarding this, any ideas?

[richo106]

3 hours ago, Chanmenie said:

You could use Illbruck sp925 or Pro Clima Aerosana Visconn Fibre, both can be brush applied, then you could seal the window to the cavity closer and the cavity closer to the blockwork. Would work out cheaper than tapes I think 

Good Idea!...Thank you

 

Looking at it, I might use tape to seal the window to the cavity closer but then use the paint for the rest. This is to ensure I get no paint on the visible area of the window

 

Edited May 31, 2023 by richo106

[nod]

You can dab onto the cavity closers two lines one against the frame the other down the edge of the block once dabed fill the gap between the reveal board and the edge of the block Then solid dab over it 

 

If your battening rough brick I would fix the batons directly to the wall Then simply staple an airtight membrane to the face of the batons Cheap and quick 

 

Theres nothing to stop you using a J bead Or a 25x15 angle fixed to the frame You will find the later easier if your not familiar with them 

Edited May 31, 2023 by nod

[Iceverge]

I would. 

 

1. Parge the walls. 

 

2. Cut a strip of membrane the length of the perimeter of the window and about 50mm deeper than the reveal depth.

 

3. Starting at the 6 O'Clock position lay the membrane on the sill, up the reveal, across the top, down the reveal and back to the 6 o clock position. Use some dabs of silicone to hold it in place. Be sure to push it well into the corners. 

 

4. Careful mark 10mm (or more depending on your window design) with a pencil around the perimeter of the window and apply your split airtight tape to seal the window to the membrane. 

 

5. Fold the 50mm remaining piece of the A/T membrane onto the wall and apply a double bead of airtight mastic to seal it to the parge coat. It may need some cutting and trimming at the corners. 

 

6. Screw a J bead to carefully cover the edge of the A/T tape on the window perimeter. 

 

7. Slot in plasterboard with a few dabs on the reverse and mechanically fix through the membrane to the brick reveals. Squirt some Illbruck FM330 behind there if you're anxious about any hollowness. You may need to use some small packers to get perfectly consistent reveals. 

 

 

I would avoid paint on airtighess near windows. You are lightly to spend longer masking it neatly than using actual airtight tape and it doesn't adhere as well either. 

 

 

 

 

Edited June 1, 2023 by Iceverge

[Iceverge]

For info, the above method works well without cavity closers for EPS blown beads, getting a really consistent and easy and cheap to install well insulated window. You can even pre install the membrane, tape and J beads before the window is in situ. 

[Dave Jones]

Just a heads up the windows would fail building regs as they have been installed. They are not set back 70% into the cavity insulation. Not too late to get them fitted correctly, use straps on the frames and fix them to internal blockwork. 

 

[richo106]

11 minutes ago, Dave Jones said:

Just a heads up the windows would fail building regs as they have been installed. They are not set back 70% into the cavity insulation. Not too late to get them fitted correctly, use straps on the frames and fix them to internal blockwork. 

 

Oh right, thanks for bringing this up. I have a quick look on the internet and as your picture shows does the window need to sit at least 30mm over the cavity?

[Dave Jones]

its Part L of building regs. also specifies the minimum U values for windows (not just the glass), do you know what your are ?

 

[richo106]

6 minutes ago, Dave Jones said:

its Part L of building regs. also specifies the minimum U values for windows (not just the glass), do you know what your are ?

 

Thank you. Does part L of the building regs apply to all building whether it’s an extension or new builds? Or just new builds? 
 

Our project is classed as an extension, even though I am going to speak to the window guys this morning but I was just wondering 

 

Many Thanks 

[Dave Jones]

applies to both, you get a poorer U value target for your windows to meet. Do you know what yours are ?

[richo106]

3 minutes ago, Dave Jones said:

applies to both, you get a poorer U value target for your windows to meet. Do you know what yours are ?

I did know, I am just trying to find it on the blurb/emails

[richo106]

3 hours ago, Dave Jones said:

applies to both, you get a poorer U value target for your windows to meet. Do you know what yours are ?

I have spoken to the window company and they said they always fit them like that due to getting a fixing into the cavity closer.

 

The u value of the windows are 1.3, this is best we could get for the style of window we wanted 

[richo106]

13 hours ago, nod said:

You can dab onto the cavity closers two lines one against the frame the other down the edge of the block once dabed fill the gap between the reveal board and the edge of the block Then solid dab over it 

 

If your battening rough brick I would fix the batons directly to the wall Then simply staple an airtight membrane to the face of the batons Cheap and quick 

 

Theres nothing to stop you using a J bead Or a 25x15 angle fixed to the frame You will find the later easier if your not familiar with them 

So the dab on the window side would sit on the cavity closer? Would the fitting be that secure?

 

I have read it a few times but can’t exactly understand what you mean. 🙈

[Dave Jones]

2 hours ago, richo106 said:

I have spoken to the window company and they said they always fit them like that due to getting a fixing into the cavity closer.

 

The u value of the windows are 1.3, this is best we could get for the style of window we wanted 

 

typical bodgit and scarper window fitters, they need to use straps and fix to the blockwork. I'd insist they refit them to comply with building standards. BCO should fail that when they come to inspect.

 

1.3 is a fail for newbuild but ok for extensions, did they send you a copy of the certification showing 1.3 as would be interesting to see.

[Iceverge]

There's plenty of space to over insulated the frames internally there. I wouldn't sweat about it. 

 

In the existing house here is what you have. @Dave Jones is right it's a nasty thermal bridge. 

 

 

 

However it's easily solved. 

 

 

 

 

 

This will do for the heads and reveals. 

 

1. A/T tape and membrane. 

2. J bead. 

3. Batten shimmed level with j bead. 

4. Membrane returned to inner wall and sealed. 

5. Plasterboard. 

6. EPS beads injected into wall as insulation. 

 

 

 

For the Window board you'll need to run some support in the form of a few battens per window as below shown inn yellow. These should be fixed to the inner blockwork. 3- 4 should be fine. 

 

 

Then let the EPS beads  Fill the rest. 

 

 

You could mess around with PIR boards etc but it's a mess. Just let the beads do the work. 

 

 

 

 

 

 

[Dave Jones]

Need a min of 150mm cav for EPS beads.

 

Messy. Much prefer sheet insulation, smaller cav better U value.

[richo106]

41 minutes ago, Dave Jones said:

 

typical bodgit and scarper window fitters, they need to use straps and fix to the blockwork. I'd insist they refit them to comply with building standards. BCO should fail that when they come to inspect.

 

1.3 is a fail for newbuild but ok for extensions, did they send you a copy of the certification showing 1.3 as would be interesting to see.

They have sent through the certificate, they are ringing me back regarding the install 

[richo106]

I won’t mention I’ve got my new shiny oak front door has a u value of 2.0🙈 things like this really highlights how much I don’t know what I’m doing 😂

 

I have attached a picture of my front, would the whole thing be treated as one? It has triple glazed (42mm) solar glass but the oak door is 57mm thick with only 20mm PIR in

Edited June 1, 2023 by richo106

[richo106]

Thank you @Thorfun

[Dave Jones]

8 minutes ago, richo106 said:

They have sent through the certificate, they are ringing me back regarding the install 

 

interesting, none of them would pass  for new build. Wonder why they bother still making them.