Cold bridging at cavity reveals and floor slab detail

[Iceverge]

4 hours ago, ADLIan said:

Sorry but that THERM model is wrong. The lintel, jambs and cill should be modelled separately effectively ignoring the window. I've not used THERM for some time but in the past it did not give the psi-value directly - the output needed more number crunching to arrive at the psi-value. Whilst the psi-value may be low in this instance I doubt that it would be negative.

 

Glad to hear any tips. I'm self taught! 

 

Anywhere to read up on it? 

 

What I was doing was taking the theoretical U value of the buildup with a perfect interface between the two and then seeing what THERM pushed out for a horizontal cut. 

 

I was being lazy here. 

I have done them separately for all the junctions of our house. Even if my calcs for the exact PSI number were incorrect I've found it very useful for just visually adjusting the junction's to minimise heat loss. 

[ADLIan]

@Iceverge

As a start you need to get copies of  BS EN 10211 (calculation methods) and BR 497 for the conventions used when undertaking linear thermal transmittance calculations. You also need to know the correct inputs into THERM and what to do with the output value (which is not automatically the psi-value unless THERM has changed recently). It is not a simple process!

[joe90]

Ha, I did no modelling, no calculations just pure logic, and it worked 👍

[Iceverge]

15 minutes ago, ADLIan said:

BS EN 10211

 

Yikes its €175!!! 

 

I'll ask santa....

[saveasteading]

On 04/04/2022 at 18:59, tonyshouse said:

I think radon goes through polythene,

I can't see any stated difference in specifications between 'radon' sheeting and other 1200guage polythene, other than certification.

Perhaps some dpm has inconsistent thickness or density, or perhaps the budget suppliers simply don't apply for the expensive test.

 

Also I have seen specifications stating ....'lay 1200 gauge polythene dpm as radon protection'....not that the designer stating this necessarily knows.

 

We are fortunate in being just outside  a radon area, and the certificate (£5 well spent) confirms this, but I did read up just in case.

The big problem would have been linking this barrier to the outdoors, when there is 600mm of existing masonry without any dpc.

Could be done by venting but very glad we don't have to.

 

I have done methane protection on big buildings (one on top of a tip)  which is much the same. Not complicated to vent it, and at 1/3 of the cost of a specialist....(who use pipes and polythene with 'methane' written on them).

 

I am not making light of the radon danger. Methane on the other hand seems to be a worry about something that has never yet happened, but could, an could be dramatic.

[dpmiller]

Radon polythene is 100% virgin as I recall.

[ruggers]

@IcevergeThank you for taking the time to add the drawings and detailed reply. Apologies for the long delay in replying, I wasn't notified and only seen them a few days ago. So with so much content, i will ask a a number of questions related.

 

1. Firstly, what is the purpose or benefit of a the OSB window box rather than just sealing the window to masonry using A/T tape plus A/T paint and applying plasterboard direct over it without the OSB? does the timber close off the cavity better helping air tightness?
    
2. You mentioned Degrading osb boxes with weather? What is going to degrade them if they are on the inside?
    
3. Do you fix your window straps to the masonry direct with OSB over the top, or is it OSB direct to masonry, and then then the window straps sandwiched between OSB & plasterboard? 
    
4. How did you fix the plasterboard to the OSB, adhesive or screwed?
    
5. Why the A/T tape between window frame and brickwork, is flexible sealant not just as good if the gap isn't too big? 
    
6. I noticed you opted for an open cell foam adhered to the external of the frame, what benefits does this offer over acoustic window foam from a gun, something like this... https://www.uksealants.co.uk/illbruck-fm330-air-tight-expanding-foam-gun-grade.html?gclid=Cj0KCQiA64GRBhCZARIsAHOLriKTW9VOqg5cwkyXSigMWuGZFUPsYyJ3RkoUdEYkdELQU9yWbMlMfHMaAsjxEALw_wcB
    
7. I'll be using flush reveals all round but this shouldn't change too much from your first example but would with the revised version.
    
8. How were the internal sills fitted, screwed from the top and filled? I've seen it done with angle brackets to the underside and then fastened to the inner face wall so no visible screw heads to be plugged or filled. Good idea but probably destructive to the wall if you ever needed to change them.
    
9. I was thinking for aesthetic reasons about adding too many layers to the inner reveal can mean the finished plasterboard face ends up close to the glazing which looks terrible. I like a equal distance around all 4 sides bet I can between finish skim and the glazing. My current home I don't like how little frame is left visible on the vertical inner reveals looking at the window.
    
10. With having building control and warranty inspections, the small angled cavity tray wouldn't be enough, they require stepped DPC or plastic cavity tray built into outer skin and resting against the inner skin with exterior weep vents. I agree on catching mortar droppings landing on the trays. Your drawing looks like the DPC is a course too low on the outside if you've used concrete lintels instead of metal insulated catnics. DPC tray shouldn't come out above the frame or it would be hard to adhere to as you mentioned.
     
11. Shot fired nails, I had to look these up, do you not require an £800 fixing gun to use these? They just fire into concrete in one shot no pilot hole?

 

[saveasteading]

24 minutes ago, ruggers said:

They just fire into concrete in one shot no pilot hole?

Yes. Often described as a Hilti gun.

They go straight into steel or concrete with no pilot.

Very nasty kick back as you might expect, and needs attention and strength.

 

The only real life issue is in going into extra hard concrete, or extra-strength steel (or too weak a material that just breaks).

There are different lengths of nails and different explosive levels too, so check for that.

 

The guns can be hired.

I seldom use them where there is any other option, especially as screws are so good these days.

[ruggers]

On 13/04/2022 at 09:40, joe90 said:

 I am in a fairly exposed location and used rockwall batts full fill(they have a BBA certificate for full fill) I also had check reveals (inner skin opening bigger than outer) to give angled reveals. Brick arches in outer skin and separate lintel internally. I made my own closures like @Iceverge shows above, window sitting on brick sills (just) and held to outer skin with stainless brackets and screws.

the only thing I would do differently if I did it again is use plaster stop bead next to the window to give a movement gap that can be filled with flexible mastic (several here have had cracking at this point like me).

@joe90Where did you mean to use the stop bead, the internal or external reveals and would you go both sides and the top? I'm guessing you mean the outside if your window straps fasten to the outer skin so as they'll of needed covered. I'm on the West coast lake district so we do get really battered in winter I've not seen anyone use anything other than timber frame or partial fill cavity

 

On 13/04/2022 at 19:22, saveasteading said:

I can't see any stated difference in specifications between 'radon' sheeting and other 1200guage polythene, other than certification.

Perhaps some dpm has inconsistent thickness or density, or perhaps the budget suppliers simply don't apply for the expensive test.

 

Also I have seen specifications stating ....'lay 1200 gauge polythene dpm as radon protection'....not that the designer stating this necessarily knows.

 

We are fortunate in being just outside  a radon area, and the certificate (£5 well spent) confirms this, but I did read up just in case.

@saveasteading i've looked at everything and can't see any noted difference other than radon usually being red or green. Both are 1200 gauge and 300mu. I'm also right on the edge of a red radon zone by map, but a report for some builds around mine the report said no radon present. Not sure how they've checked. Can't imagine any houses that already built checking.

On 13/04/2022 at 21:46, dpmiller said:

Radon polythene is 100% virgin as I recall.

@dpmiller Seems like some still use recycled. https://www.plastics-express.co.uk/dpm-1200-gauge

[ruggers]

1 hour ago, saveasteading said:

The guns can be hired.

I seldom use them where there is any other option, especially as screws are so good these days.

Good to know they hire them if need be. For the little use I'd need one for but concrete screws probably do the job for me. Very impressive though they can puncture through thick steel or stone. 

 

I've got a mate who fits suspended ceilings and i think they might use something similar.

[saveasteading]

3 minutes ago, ruggers said:

puncture through thick steel or stone. 

Predrill, and use self-tapping screws  (concrete or steel specific) or plugs.

 

12 minutes ago, ruggers said:

radon zone by map

https://www.bgs.ac.uk/datasets/radon-data-indicative-atlas-of-radon/

is the simplest, and there is a link to buy a certificate for your postcode. £5.

[joe90]

27 minutes ago, ruggers said:

joe90Where did you mean to use the stop bead, the internal or external reveals and would you go both sides and the top?

Inside, wherever the plasterboard joins with the window, my windows are wooden, hard wood but wood still moves a little fill the small gap between stop bead and window with flexible mastic. Even our Jeremy had problems with plaster cracking here and wished he had heard of this before.

[ruggers]

Can you not just seal the board to the frame same as you would using the stop bead. What advantages does the stop bead offer if it's getting a bead of sealant anyway.

[Iceverge]

On 29/04/2022 at 13:16, ruggers said:

Firstly, what is the purpose or benefit of a the OSB window box rather than just sealing the window to masonry using A/T tape plus A/T paint and applying plasterboard direct over it without the OSB? does the timber close off the cavity better helping air tightness?

 

Robustness, membranes get torn by careless follow on trades. You can use a membrane j beads  and just plasterboard as per https://www.edmondodonoghue.com/build-it-better-window-door-detailing/

 

On 29/04/2022 at 13:16, ruggers said:

You mentioned Degrading osb boxes with weather? What is going to degrade them if they are on the inside?

 

This can happen if you build the inner leaf before the outer and install the window boxes first. The ply greenbuilding store used on denby dale delaminated before the windows were installed and the outer leaf was finished. It's not an issue with fitting the OSB post windows. 

 

On 29/04/2022 at 13:16, ruggers said:

Do you fix your window straps to the masonry direct with OSB over the top, or is it OSB direct to masonry, and then then the window straps sandwiched between OSB & plasterboard? 
 

 

No window straps were used. The windows were bolted to the outer leaf with 90deg angle brackets.

 

On 29/04/2022 at 13:16, ruggers said:

How did you fix the plasterboard to the OSB, adhesive or screwed?

 

Screwed, but either should be fine. 

 

On 29/04/2022 at 13:16, ruggers said:

Why the A/T tape between window frame and brickwork, is flexible sealant not just as good if the gap isn't too big?

 

I'm not sure what you're referring to here. do you mean the osb window bucks and the bricks? 

 

In any case you would need to use proper airtight sealant, not off the shelf mastic as that can dry out over time and crack. Airtight sealant is like trying to work with bubble gum. It's very sticky and messy. Tape is clean and easy. Having seen the bond by sealants, airtight paint and airtight tape I would rate the tape best for adhesion. 

 

On 29/04/2022 at 13:16, ruggers said:

I noticed you opted for an open cell foam adhered to the external of the frame, what benefits does this offer over acoustic window foam from a gun, something like this... https://www.uksealants.co.uk/illbruck-fm330-air-tight-expanding-foam-gun-grade.html?gclid=Cj0KCQiA64GRBhCZARIsAHOLriKTW9VOqg5cwkyXSigMWuGZFUPsYyJ3RkoUdEYkdELQU9yWbMlMfHMaAsjxEALw_wcB

 

Expanding foam is another pet hate for me. Messy, it shrinks unless you get very good stuff, it's expensive.  I think you're referring to Compriband which is an expanding foam strip. Very clean and robust and will last as long as the windows. Also overlapping the frame with the brick and using this will create very sound proof windows. 

 

https://www.sealantsonline.co.uk/ProductGrp/002a005a0001

 

 

On 29/04/2022 at 13:16, ruggers said:

I'll be using flush reveals all round but this shouldn't change too much from your first example but would with the revised version.

 

I don't follow you here. What wouldn't work? Maybe a diagram would help me see it. 

 

On 29/04/2022 at 13:16, ruggers said:

How were the internal sills fitted, screwed from the top and filled? I've seen it done with angle brackets to the underside and then fastened to the inner face wall so no visible screw heads to be plugged or filled. Good idea but probably destructive to the wall if you ever needed to change them.

 

Glued onto the OSB base of the window box. 

 

On 29/04/2022 at 13:16, ruggers said:

I was thinking for aesthetic reasons about adding too many layers to the inner reveal can mean the finished plasterboard face ends up close to the glazing which looks terrible. I like a equal distance around all 4 sides bet I can between finish skim and the glazing. My current home I don't like how little frame is left visible on the vertical inner reveals looking at the window.

 

Thermally it's preferable to bury as much of the frame in the insulation as possible. With the revised method I've shown the gap should be equal 3 sides and maybe slightly less at the bottom as sills are normally thinker than plasterboard. 

On 29/04/2022 at 13:16, ruggers said:

With having building control and warranty inspections, the small angled cavity tray wouldn't be enough, they require stepped DPC or plastic cavity tray built into outer skin and resting against the inner skin with exterior weep vents.

 

This thinking is based on old narrow cavities. To enforce the tray to fully cross the cavity suggests that the insulation will be wet right to the inner leaf. If this is the case you've got much more serious problems, Practically I cannot see any issue with an angled profile extending 50mm-100mm in from the outer leaf and a gap to the inner leaf.  I can't see the benefit of weep holes. How much water are they expecting to make inside the wall? The outer leaf should be well pointed such nothing more than the smallest drips form on the inside of the outer leaf. These will be directed to either side of the window by my PVC profile and drain harmlessly to the bottom of the cavity. If you are in a very exposed location and wind driven rain is really such a large factor, right above the window is the last place you want to introduce more holes. 

 

 

On 29/04/2022 at 13:16, ruggers said:

Your drawing looks like the DPC is a course too low on the outside if you've used concrete lintels instead of metal insulated catnics. DPC tray shouldn't come out above the frame or it would be hard to adhere to as you mentioned.

 

Are you working from the revised detail? I wouldn't build it again the same as we have done. 

 

 

On 29/04/2022 at 13:16, ruggers said:

Shot fired nails, I had to look these up, do you not require an £800 fixing gun to use these? They just fire into concrete in one shot no pilot hole?

 

Yup. Rent one as people say. You could do the whole thing in a few hours if you had your OSB pre fixed to the frames. 

 

https://www.olympustoolhire.co.uk/product/cartridge-fixing-tool-nail-gun-steel-masonary-concrete/

 

[ruggers]

On 02/05/2022 at 11:19, Iceverge said:

No window straps were used. The windows were bolted to the outer leaf with 90deg angle brackets.

 I see what you mean now after looking back, easier method with tapered reveals. Is that a standard window detail or something different (Looks like 2 squares)?

On 02/05/2022 at 11:19, Iceverge said:

Expanding foam is another pet hate for me. Messy, it shrinks unless you get very good stuff, it's expensive.  I think you're referring to Compriband which is an expanding foam strip. Very clean and robust and will last as long as the windows. Also overlapping the frame with the brick and using this will create very sound proof windows. 

 

https://www.sealantsonline.co.uk/ProductGrp/002a005a0001

I'd not heard of compreband expanding seal adhesive foam. I thought it was just the standard stick on foam strip. Whats the working time on the foam expanding? Did you fit it prior to fitting the frames or afterwards. I was thinking prior would make it too hard to fit air bags between frame and brick work when installing.

On 02/05/2022 at 11:19, Iceverge said:

I don't follow you here. What wouldn't work? Maybe a diagram would help me see it. 

I just meant my inner and outer skin will be the same width apart, square reveals not chamfered back like yours. the checked reveal shown here does look a good idea but i'm unsure what the frame bears down onto when not using a precast sill as it would just be hovering over the cavity. My UPVC frames were just going to rest partially on to the outer leaf. (No stone sills)

 

On 02/05/2022 at 11:19, Iceverge said:

Thermally it's preferable to bury as much of the frame in the insulation as possible. With the revised method I've shown the gap should be equal 3 sides and maybe slightly less at the bottom as sills are normally thinker than plasterboard. 

 

This thinking is based on old narrow cavities. To enforce the tray to fully cross the cavity suggests that the insulation will be wet right to the inner leaf. If this is the case you've got much more serious problems, Practically I cannot see any issue with an angled profile extending 50mm-100mm in from the outer leaf and a gap to the inner leaf.  I can't see the benefit of weep holes. How much water are they expecting to make inside the wall? The outer leaf should be well pointed such nothing more than the smallest drips form on the inside of the outer leaf. These will be directed to either side of the window by my PVC profile and drain harmlessly to the bottom of the cavity. If you are in a very exposed location and wind driven rain is really such a large factor, right above the window is the last place you want to introduce more holes. 

I agree with you on this, but with B.C being involved and warranty inspections, I wouldn't get away with a 50mm angle, they even like DPC turned up ends or on the trays to prevent water run off to the sides. As you say, they will just collect all mortar and weep holes could be blocked from the inside. Even the best bricky can't prevent it dropped down the inner.

[saveasteading]

12 minutes ago, ruggers said:

I'd not heard of Compriband expanding seal adhesive foam

Used in bridges and dams at the top end of the range. So dense that it needs a machine to compress it and takes hours to expand back. So don't choose that spec.

It is addictive to compress offcuts and watch the thing expanding again.

[ruggers]

I'll try & get a sample of some. I was just curious to how long it took to expand once took off the roll and applied to the window frame, and whether or not you apply before or after the fit. A youtube video shown it being fit afterwards but looked fiddly. Is the roll useless once opened?

[ruggers]

The regs say that building regulation part B requires you to have fire rated cavity closers. Is this something new as some of you have used your own methods, ie: PIR jammed between or premade plastic closers?

[Rishard]

I’ve used compriband tape for a lot of green oak frames. It’s great at adjusting to the movement of the oak. Once you have opened the roll you can cut off what you need and tape the roll together to stop it expanding. Keep it flat and stored well as once it gets uncoiled it’s worthless. They come in varying widths and expansion thickness to suit all sorts of applications. I used to apply it to the frame and compress the glass on to it. On the outside I would stick it to the cover board and compress it onto the glass. You have a few minutes to get it stuck on before it starts expanding. Easy enough when your prepared. Haven’t tried retro fitting into gaps but don’t see it being an issue. 

[Rishard]

This could be used for retro fit possibly. 
 

https://www.illbruck.com/en_GB/product/tp601-compriband-e/