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What and where to use air tight tapes on block built house


JamieM
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Hi

 

I’m in the middle of my build (at the watertight stage) and in the middle of having first fix completed.  I probably should have been thinking about the air tightness tapes before now but haven’t had the chance.

 

My question is, where should I be using them? (I know the answer is anywhere there might be air leaking). But would anyone have a list (especially if there are any less obvious areas)? Are there lots of different tapes to use depending on what is being taped to. I.e. block vs plasterboard?

 

Also, are there foams that can be used or are these prone to shrinkage over time?

 

Bit of background on the build

 

The windows/doors are descent enough - triple glazed with no trickle vents.

The house is going to be externally rendered.

There is a Cold roof with MHRV.

Downstairs walls are block, upstairs is a mix of block and stud.

The block walls will be plastered and the stud walls will be palsterboard and then skimmed.  

Based in NI and house is going to be long term home

 

thanks

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Normally you'd have an air tightness strategy which identified the continuous layer around your house that is air tight. You then use the tapes as just one means of ensuring that layer is continuous. For example, you might use them around the window frames.

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I used a membrane underneath the plasterboard which gets bonded to the blockwork using a special glue. The other areas are the doors and windows. Then it's all the penetrating services that need sealed round. 

http://www.cleanenergyireland.ie/air-tightness/

Good video of the membrane and window tape here. I bought all my stuff from these guys as well.

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1 hour ago, JamieM said:

The block walls will be plastered and the stud walls will be plasterboard and then skimmed.  

 

@tonyshouse is one guy that posts here and been through this though there maybe others.  If you want high levels of airtightness with a block wall then you are going to have to use the inner face of the blockwork as the VCL / airtightness layer.  It is very easy in the laying of blockwork to leave or to create fine air  paths between blocks.  A direct inner render coat or plaster coat will help to minimise these, but the danger zones are the floor voids and joist hangers which tend to be omitted when planning plastering, as well as the window, door and services openings discussed in previous posts. 

 

The best time to address airtightness in the floor voids is during construction, but you are now past this, so the next best time is before boarding out. If you don't bother then at best you will get very modest airtightness by sealing around skirting, etc.

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1 hour ago, TerryE said:

If you want high levels of airtightness with a block wall then you are going to have to use the inner face of the blockwork as the VCL / airtightness layer. 

 

Can you provide a citation or explanation for that? The inner face bit I mean. In the case of a cold loft I can see why you'd say that, but if you are going full tea cosy on a house, why not join the outer face of the outer blockwork to the air tight layer on the warm roof? If anything I'd have thought that's easier than joining it to the inner face, because then you have to get past the timber in the roof structure somehow.

Edited by gravelld
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The three separate bits in a block build all need joined together to get very good airtightness. The floor, the walls and the ceiling. For the floor you will have a layer of dpc sticking out under the bottom course of block to which you can seal the DPM to when you do your screed. Another way if you do the finished floor first is to lap the DPM over the blocks and then put the dpc on and build away. You can also use a tape to join the finished floor to the wall.

The wall and ceiling junction you can use a membrane fixed to the joists and then glued to the blockwork. When it gets wet plastered then the wall gets sealed in. If you just rely on plastering up to the ceiling wall junction once your house dries out and cracks here then you will have holes in the fabric. 

The rest are all the holes in the walls and ceilings that need sealed up. For Windows and doors you use a tape that sticks to the frame and then is glued to the blockwork. All the services then need sealed up with tape or sealant depending on what it is. 

The hardest area is round joists where the best?? Method is the like of the Tony tray. Similarly the eaves are a little more tricky if you go for attic truss.

All it requires is a bit of thought and not excepting poor/lazy trades putting holes in the fabric if they don't have to.

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To be honest, I not the expert here. I was just relating of detailed conversations with a couple of crews who worked on my timberframe house (both of which had a lot of experience of erecting passive house class both blockwork and timberframe constructions, and these crews essentially gave the same message that Tony described in his blog here, and this was that trying to achieve airtightness in the floor void zone was a real PITA if you didn't do something to actively address this (such as the sock method that Tony used). Whether you sit your joists in the block skin or use hangers the material interface invariably causes separation of the mortar at opens many cracks through the blockwork.  These are structurally insignificant, but can really impact the overall airtightness.  Essentially the house will leak like a sieve.   As JSH once mentioned, if either of our houses was totally airtight except a 1" diameter hole somewhere, then it would fail a 0.6 ACH airtightness test.

 

Just out of interest, here is how they did it on our TF build: the floor was decked out to the external perimeter and the airtighness membrane looped back onto it before the next storey cassettes where craned into position.  I am not saying that everyone wants or needs to achieve an 0.6 ACH figure, but more that some though about how you seal the internal floor void surface of the exterior walls will have a major impact on the actual airtightness achieved.

IMG_20151108_150432973_HDR.jpg

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Cheers guys. I didn't (as I was too late/unorganised) get the chance to put in the tony trays between the joists when they were installed which is a shame as it looks like a great idea. Is there anything I can do now to rectify it (I know there's possibly no perfect way to fix it)? Floorboards are in but the plasterboard isn't on yet.

Or would it make any sense to tape the floor boards at all the joins? Currently they are glued.

My joists are built in to the inner wall with cement round them.

We don't have attic trusses.

 

Thanks for all your comments and thanks @Declan52 for the description of what you did. Going to look at that website and associated videos now.

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Over time the joists flex as they shrink and expand so the cement will crack. You could put tape all the way round each gap or even cut some pir insulation and stick it to the blocks and then tape the edges. You will have to tape from you floor above to the wall and then plaster over this to seal it in. The window tape on that link can do this.

It will take a fair bit of time to do it right but would be well worth it. 

Are you filling the joists with rockwool???

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Yes, there will be Rockwool in between the joists.

 

Good point about the joists flexing.

 

Calling down to site later today. Will have a look at the joists properly and look at the amount of tapping that would be required. Does sound like a lot of work. 

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Not hard work just time consuming. A good two days cutting and taping. You don't have to do it  and just accept the heat loss, your call. Just use any insulation you have lying about. Can be sheet insulation or even cavity wall boards. 

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Sorry I am late to this thread but I am dealing with this issue myself on our build and we are doing it this way. We are using Finn joists and using built in hangers on block work ( the builder is already aware of air leakage through timber shrinkage if joists are inserted in a wall) I am getting the builder to parge an area equivalent (plus a bit) to the joists, so that when the house is plastered this airtight layer is continuos behind the first floor. I would like to seal the hangers where they penetrate this parged layer but not sure if air leakage would be much of a problem as steel does not shrink and warp like timber.

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Yup,Tony also mentioned the alternative of using hangers plus sealant, but be aware that you can get air leaks particularly in the risers between blocks if not fully filled; that's why the render suggestion is made. Alternatively is you haven't hung the joists just hang a strip of air tightness membrane around the wall at floor void level and punch the hangers through it and seal each one.  

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So I’ve had a look at the website you recommended Declan.

 

As I see it (and happy for anyone to point out if I am wrong) below are the tapes I would require.

 

Windows

http://www.cleanenergyireland.ie/air-tightness/products/window-and-door-tapes/winflex-i-interior-window-reveal-tape/

 

for around services i.e. heat recovery pipes penetrating ceiling etc

http://www.cleanenergyireland.ie/air-tightness/products/air-tightness-tape/gerband-586-uni-tape/

 

Ground floor to wall

http://www.cleanenergyireland.ie/air-tightness/products/window-and-door-tapes/win-50-50-split-release/

 

I had a look at my joists over the weekend (picture attached) and it would not  be possible to tape all around the joists – as the floor boards are already in I wouldn’t be able to tape around the top of the joists. Would it be possible instead to use tape on the 1st floor on the floor boards to the wall thus sealing the upstairs rooms ( and downstairs ceiling the ceiling plasterboard to the wall thus sealing downstairs)?

 

@Declan52did you buy off the company direct or do they supply through my local BM?  I’m just curious about pricing and (also calculating the amount a I require although that would be pretty much measuring the linear distance and adding 10% or so)

 

thanks

joists.jpg

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The green tape is used for the joins on any membrane as well. The window tape has a small tacky side that sticks to the window but you need the fortax 6400 to glue it to the blocks. 

I just sent them an email with the linear meters on it and they worked it out. Sent the cheque of and the goods arrived. 

Taping the floor above and below is probably your only option now.

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Can a skim on plaster board be used as an air tight seal?

I assume the membrane that declan used would be a better approach. But just thought I'd ask if people used just plaster board and skim finish for ceilings? (And whether they got a half decent air tightness or not?)

Thanks

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  • 5 years later...
On 20/01/2017 at 16:49, Declan52 said:

a membrane underneath the plasterboard which gets bonded to the blockwork using a special glue.

What is the name of the special glue please?

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