WWilts

Airtight walls & fixing stuff to them

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Airtightness required 4.0
Not against doing better, of course. But cost control is a priority.

 

Two storey. Block inner leaf of cavity wall. Initial design is plasterboard on dabs.

What materials would you advise to maintain airtightness? Damp-proof membrane seems the front runner. But where exactly in the wall layers? Or what else that is reasonably priced?
How would you run services so that it all looked neat?
What approach would you take to allow attachment of reasonably heavy stuff to walls in future?

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For services, forget dot and dab.  Fix an airtight membrane to the wall with 25 by 50mm battens vertically every 400mm.  Run all pipes and cables in that service void created by the battens then screw plasterboard to the battens.

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41 minutes ago, ProDave said:

Fix an airtight membrane to the wall with 25 by 50mm battens vertically every 400mm.

This seems like a way to include internal insulation too. Improving the walls U value.
How do folks with internal insulation run services through the void?

Would fixing battens over the airtight membrane involve creating airleaks in the membrane?

 

Edited by WWilts

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What Dave says I used 35mm thick timber as I needed 47mm deep boxes for cooker points and data points.

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Improving the airtightness is probably the best bang for your buck. 

Good details don’t cost much, £5-600 in tape and membranes is a good insurance policy for a better house. 

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2 hours ago, Russell griffiths said:

I thought you wanted to improve the airtightness

Alternative approach instead of airtight membrane:
Internal airtight layer - Plasterboard with tape to seal joins. Plasterboard is in the equation already

Has anyone found plasterboard + tape ok for airtightness?

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6 hours ago, WWilts said:

Alternative approach instead of airtight membrane:
Internal airtight layer - Plasterboard with tape to seal joins. Plasterboard is in the equation already

Has anyone found plasterboard + tape ok for airtightness?

It works if done correctly, boards have to be fitted with full strips of adhesive, not dabs, all back boxes need fully sealing, any penetrations sealed. 

Its all about getting the details right. 

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Biggest thing to help would be a wall plate vs cutting the joist ends into the inner leaf of block. Then, a job you can do yourself, is to parge the entire internal face of the inner leaf with a cement slurry mix, applied by brush in most instances, to seal the pores of the block. Chases for cabling are not necessary if you are dabbing boards on, but the boxes will need to be recessed according to final finish depth of boards. If you do have to chase, then they get fully filled back in to maintain airtightness. 

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9 hours ago, Nickfromwales said:

wall plate vs cutting the joist ends into the inner leaf of block.

Tks. Is that the same as Joist Hangers? 
Still trying to learn the terms.
 

9 hours ago, Nickfromwales said:

If you do have to chase, then they get fully filled back in to maintain airtightness.

Plumbing is main worry. 
"Fully filled back in". Does that mean plastering to fill in gaps that remain?
Apologies for being so ignorant about the terms used.
 

 

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10 hours ago, WWilts said:

Is that the same as Joist Hangers? 
Still trying to learn the terms.

Wall plate is a continuous timber at the ends of the room where the joist ends connect eg instead of cutting into the inner leaf. Joist hangers would be used in conjunction with the wall plates ;)  

10 hours ago, WWilts said:

Plumbing is main worry

Why? Most will be surface mounted and boxed, but can be dabbed over. Usually not as the dab would be quite deep. Same for pipes and cables, chase and bury in strategic places, but cable chases would be back filled with parge and plumbing chases would be foamed to insulate the pipes from their surroundings. 

10 hours ago, WWilts said:

"Fully filled back in". Does that mean plastering to fill in gaps that remain?

Yup. Air will travel through switches and sockets and into the chases. 

 

10 hours ago, WWilts said:

Apologies for being so ignorant about the terms used

The stupid questions are the ones you didn’t ask. “Apologise yea’ not.”

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On 22/02/2021 at 12:57, Nickfromwales said:

Biggest thing to help would be a wall plate vs cutting the joist ends into the inner leaf of block. Then, a job you can do yourself, is to parge the entire internal face of the inner leaf with a cement slurry mix, applied by brush in most instances, to seal the pores of the block. Chases for cabling are not necessary if you are dabbing boards on, but the boxes will need to be recessed according to final finish depth of boards. If you do have to chase, then they get fully filled back in to maintain airtightness. 

 

Would this be good to use? Tanking Slurry Waterproof Cement Based Coating 20kg | Builders Merchant Direct (bmdgroup.co.uk)

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@nod  

Is there any need to be paying £20 a bag for slurry? Cant this just be a few quid bag-o-cheapo-cement and a bit of additive to DIY mix?

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1 minute ago, Nickfromwales said:

@nod  

Is there any need to be paying £20 a bag for slurry? Cant this just be a few quid bag-o-cheapo-cement and a bit of additive to DIY mix?

 

The Parge coat we often use is more for sound deadening 

I never call it an airtight coat as it gives the impression that the dry liners don’t need to seal everything 

So we always call it sound coat 

So yes any kind of slurry is fine 3-1 stipple with a stiff brush will do the job 

Save £££

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1 minute ago, Nickfromwales said:

 

Bingo. No £20 a bag necessary. 

No 

We do it because it’s on the spec 

Nearly always housing association 

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