Cavity wall draughts

[TheBeliskner]

Hi,

 

We live in a house that's half 1920's and half 2008. The old part of the house is great, no major issues, the new part has a fibre filled cavity wall with rendered concrete block outer and aerated concrete block inner. The house his fairly exposed at the top of a hill and it gets pretty damn windy.

 

2 upstairs rooms on the new end of the house are colder than the rest, even the downstairs room is a little colder but more manageable. It's certainly not loft insulation as there's 400mm up there. I had to drill a hole through the wall recently and as soon as I reached the cavity I could feel a fairly significant breaze coming through. I lifted a corner of carpet and put a hole through there too and I can feel the breeze under the floor too. 

 

Is it normal to have that much airflow in a cavity and/or under the floor? If not any suggestions on how to find the cause and fix it?

 

Take a guess which rooms are at the new end.

 

Edited December 5, 2021 by TheBeliskner
More clarity

[ProDave]

By 2008 building regs required a cavity to be ventilated.  Unfortunately most builders have no idea about air tightness and you will have lots of leaks between the cavity and the inside of the house, most likely joist ends, poorly pointed blockwork that won't even have been plastered in the inter floor area etc.

 

Sadly no easy fix.  It's what I say about most of the UK housing stock is built to really poor standards, even some quite recently built houses.  It's the sort of detail that is easy to get right when building, if you know what to do and can be bothered.

[TheBeliskner]

2 minutes ago, ProDave said:

most likely joist ends, poorly pointed blockwork that won't even have been plastered in the inter floor area etc.

 

I've been considering lifting part of the floor to solve a few squeaky boards. It sounds like a might as well lift all of it and and break out the expanding foam? 

[nod]

Whilst this doesn’t help this poster 

Airtightness on new build is so easily achieved 

Blocks should be pointed properly 

and all ceilings and studs should be acoustic sealed against the wall 

If every edge of the boards dabbed on are sealed No air should circulated behind them Also all sockets and switches should be sealed 

It still mystifies me that none commercial TF homes don’t use fire rated baffle boxes behind sockets and switches 

I pay £5 per baffle Made and fitted

 

The rules need to be tightened Get rid of the corrupt air testers that are all competing for the same business 

[ProDave]

Is this house "plastered on the hard" or dry lines with plasterboard?

[TheBeliskner]

6 minutes ago, ProDave said:

Is this house "plastered on the hard" or dry lines with plasterboard?

I've no idea what that means exactly but I'm guessing you want to know how it's plastered. It appears to be dot and dab plasterboard onto the block work. 

 

What we didn't discover until after we moved in was that the extension was self build by a builder and we've found some oddities. There was a rat problem, the previous owners told us it was fixed but it wasn't, ultimately it was caused by unsealed redundant drains. There was also an old boiler that was bodge installed and the person who installed it denied having ever done it even though their name was on the paperwork and nobody could provide any invoice to prove who did it. Before we moved we knew there was no electrical certs but we planned to change a few things anyway so that was fine, when the electrician's came to do our work they described it as "builder electrics" with the only redeeming feature being that at least all the circuits had continuity. 

 

Poor airtightness seems like par for the course at this point. 

[ProDave]

Dot and dab plasterboard as @nod has said can be done properly.  But all too often the plasterboard is just fixed on blobs of glue with no detail thought about.  the result is the top and bottom of the gap behind the plasterboard is often left open to the cold loft space, cold inter floor area and even sometimes cold under floor area if a downstairs suspended floor.  This creates what has become known on here as a "plasterboard tent" where cold air can circulate behind the plasterboard and negate any insulation in the walls.

 

It is so frustrating to see this time and time again as it appears the vast majority of builders don't know or understand the problem and the relatively simple way of avoiding it is to ensure a continuous seal of adhesive along the edges of a board.

 

It sounds like yours was build by a typical didn't care or didn't know type builder.

[tonyshouse]

Here is some info on the problem and possible methods of rectification, I am working on innovative methods too

 

https://readinguk.org/draughtbusters/going-further/dot-and-dab/

[TheBeliskner]

I've not seen any evidence of air circulating behind the plasterboard, the sockets I've taken off are draught free so that's some small win then.

 

Thanks for the advice. I think I'll lift the floor around the edges in the new year and seal up any gaps I find. When I get to refurbishing the bathroom next year I wasn't planning on pulling up the floor but I think I'll do it now so I can seal up the gaps. Might even make use of the opportunity to put in some insulation in the suspended floor and some underfloor heating. Busy year next year!

[joe90]

1 hour ago, ProDave said:

It is so frustrating to see this time and time again as it appears the vast majority of builders don't know or understand the problem and the relatively simple way of avoiding it is to ensure a continuous seal of adhesive along the edges of a board.

Which is why (I think) the majority of us on this forum are self builders to make sure it is done right ?

[tonyshouse]

The whole philosophy of cavity walls has a basic flaw in it and we are having to live with the energy use and comfort impacts of going down thar route.

 

Design is important and as a nation we have got it wrong and won’t admit it or change.  But why? 

[Radian]

4 hours ago, TheBeliskner said:

We live in a house that's half 1920's and half 2008. The old part of the house is great, no major issues, the new part has a fibre filled cavity wall with rendered concrete block outer and aerated concrete block inner. The house his fairly exposed at the top of a hill and it gets pretty damn windy.

 

I wonder if the fibre filled cavity performing as it should? Unless the outer leaf is rendered in K Rend I'd be concerned about wind-driven rain in your location - where abouts are you?

[tonyshouse]

All cavities are draughty and fibre is also use in air filters. 
 

 

[ADLIan]

Mineral wool cavity batt /blown in at a density of at least 18 kg/m3 is normally enough to prevent air movement in a fully filled cavity.

[tonyshouse]

Therein lies one problem, rarely fully filled, leave a gap between the soffit and the wall plate and all is lost air from outdoors in between the blocks and plasterboard 

 

gaps around joist or beam ends will leak draughts into the floor void 

[ADLIan]

Incorrect install of plasterboard on dabs is another matter. Mineral wool cavity batt normally quite forgiving to quality of workmanship. Blown in open to problems if all cavity/voids not fully filled which is very difficulty to verify.

[TheBeliskner]

9 hours ago, Radian said:

 

I wonder if the fibre filled cavity performing as it should? Unless the outer leaf is rendered in K Rend I'd be concerned about wind-driven rain in your location - where abouts are you?

 

Hertfordshire. The house has a full external render with wooden cladding on the top half. Roof is a bit of a weird design as it extends down past the ceiling of the house so we have the angle of the roof around the edges of rooms and windows have small flat roofs protruding out. 

 

No evidence of damp insulation when I've been fishing around in the walls. 

Edited December 5, 2021 by TheBeliskner

[Seeoda]

On 05/12/2021 at 13:55, TheBeliskner said:

I've not seen any evidence of air circulating behind the plasterboard, the sockets I've taken off are draught free so that's some small win then.

 

Thanks for the advice. I think I'll lift the floor around the edges in the new year and seal up any gaps I find. When I get to refurbishing the bathroom next year I wasn't planning on pulling up the floor but I think I'll do it now so I can seal up the gaps. Might even make use of the opportunity to put in some insulation in the suspended floor and some underfloor heating. Busy year next year!

Although perhaps the bulk of your draughts do not seem to come through your inner leaf wall, I imagine some is. Ripping down the dot and dab  and applying airtightness paint or parging is a pain and expensive but it is worth it in the long run. Maybe do it in the summer time for comfort.