Draughty walls.....

[centricx]

Have brick-built barn, which has been previously converted by putting timber studding about 30cm from inner brick wall and covering with Kingspan.

2 of the rooms are at angles to the rest of the building and are much colder, both single story with vaulted ceilings. Both have huge draughts behind the Kingspan, which is the cause of the cold.

When I look in and up through an access hatch, I can see odd bits of plant growing through from the outside into the void (now removed) but it suggests strongly that there is simply a gap all the way up to the roof, and that the wind gets under the roof (necessary for ventilation in that space, I believe), but then whistles around the walls too.

So, how do I better stop the draughts? do I fill the upper gap, just below the soffits, with expanding foam to make it more airtight for the walls itself - or do they need the draught for ventilation? I understand I can't use cavity wall insulation as it's pressing against timberframe and plasterboard, and I'm not able to remove the walls for any other sort of fix.

I've made it better by ensuring the back boxes are fitted well so there are fewer draughts into the room itself, but the walls themselves are noticeably colder than in other parts of the house.

 

[robinbanks]

How thick is the kingspan? How do you assess "noticeably colder"?

 

[robinbanks]

I understand I can't use cavity wall insulation as it's pressing against timberframe and plasterboard,

I'm confused as to why there isn't any kingspan in between the cavity and the plasterboard? Why would CWI press against plasterboard?

 

[centricx]

the plasterboard is standard plasterboard with approx 3" thick kingspan (celotex?) on the back, with the void being behind that. Draughty means cold blast-of air if backbox removed, and walls are noticeably cooler to touch than other walls in house, and room temp is noticeably low

 

[centricx]

put another way, what's the accepted construction method near the roof for such a frame inside brick walls? Seal across horizontally, or let air flow everywhere?

 

[robinbanks]

I'm of the opinion that a wall with a wedge of insulation up the back of it doesn't need to be ventilated on the insulated side

 

[burtlad]

We have a similar issue to the original post.

Brick built barn converted about 5 years ago, heated by ashp and underfloor upstairs and downstairs.

The brick barn has a cavity, which was left empty when converting as the walls were all studded out and insulated with kingspan, approx 200-300mm air gap was left between the dry lining and the inner block wall.

We pulled our builder up on draughts as it was being built, he begrudgingly fitted a membrane after our complaints ut this was done over the top of the kingspan before being boarded out and plastered. They also membraned across the ceilings and taped all joints.

Once complete the draughts were still terrible, through sockets, downlighters and anywhere where there were gaps.
I spent months caulking, taping back boxes, down light holes, and foam filling anything else (such as where floorboards met the walls under the bath where on a windy day it would blow a candle out).
On a windy cold day in the wrong direction then 3 rooms won't go above 15 degrees with heating flat out, so had to resort to electric radiators in our baby's room when it's very cold!

We found that not running the upstairs underfloor heating was more efficient, as the draughts were carrying the heat out of the void and outside, rather than through the floorboards.
As its air source heat pump we have limited capacity on thermal input so these losses mean £1000+ per month heating bills in the cold months

We had the outer wall cavity filled with insulation to see if this helped, it made a slight improvement but still not great

Today I put a smoke bomb above the ceiling in one of the worst rooms, taped all holes to see where it escaped on a still day. From outside the house smoke rose through the roof tiles and around the velux windows, mvhr vents and this spread over a large area above the room.

Should we now have the roof off and re felt with modern membrane and seal to the top of the wall plate and across to the dry lined cavity? The roof was not replaced during the build as was only around 25 years old, but had old non breathable felt so we knew it would need doing one day.

Any advice please, dos or don't? I was going to speak to a local trusted roofing contractor for their opinions

Thanks

Rob

 

[robinbanks]

Oof, what a shame; the opportunity to nail this was there at construction time by putting a membrane on the outside of the panels before they were stood up and fixed together. Gutting that your builder was monumentally incompetent but it's an oft repeated story; the majority of trades just don't understand the sentiment of the words "build tight, ventilate right", if they've even heard of them

That the sockets are draughty seems evidence that cold world air can reach the back of the plasterboard the socket is mounted in, which means the reasonable insulating effect the kingspan can have is seriously diminished if it's being bypassed

What kind of insulation did you have the cavity filled with? Was it well applied? Are you saying your wall buildup is now:

World
Stone wall
Filled cavity
Block skin
Clear cavity
Stud wall with king span between
Membrane, full of holes
Plasterboard
Room

?

Regards the smoke test, are you saying you e.g removed a down lighter and put the smoker into the ceiling void above the room, and were later able to see the smoke filtering through the roof tiles? Describe the insulation that exists between the ceiling plasterboard of the room, and the surface of the tiles, because you seem to be implying you don't have any?!

 

[burtlad]

Hi Robin,

Thanks for the reply.

Yes it is massively frustrating that this should have been done at the time of build correctly, a main contractor was incompetent and pig headed in many ways, combined with a seperate renewable energy supplier who did all heating parts that didnt communicate very well, its left us with an inefficient and expensive end result.

Your description of the make up is correct

World
Stone wall
Filled cavity ( blown fibre, this was checked by the seperate contractor from a company we trust)
Block skin
Clear cavity
Stud wall with king span between
Membrane, full of holes
Plasterboard
Room

I think your question on the space between the ceiling void and the tiles is the unknown i also have. Without pulling ceilings down or removing the roof its a bit unclear, but there appears to be a path that this smoke and the draughts can pass through from what should be the warm suspended underfloor heating pipes and trays, to the outside world

I suppose my question is should we have the whole roof off and re felt with breathable but current spec membrane, or do you think removing part of the roof where it meets the walls and packing with more insulation in the intersection area alone would suffice?
Maybe some additional membrane to be applied to these regions also?

Are there any issues we can cause here by sealing up too much? We have the mvhr units which should help internally but dont want to cause any damp in other parts of the structure!

Ive done a rough sketch to what i think we have based on memory, checks and photos during the build. From this the solution appears easy, but practically this is going to be expensive and time consuming so wanted to see if people thought this would solve the issue and be worthwhile!

Hopefully no one else encounters the same issues which have plagued us sin e the place was completed.

 

[robinbanks]

Where you are right now, I'd fill that cavity; it's clear it's circulating air and the cavity fill you've already had done is nigh on ineffective as a result. At the top of the walls inside the circle of unknown area is a problem that needs resolving (filling up with an insulation that inhibits air movement)
The easiest access to it might be by stripping the lower roof :/

A better wall buildup would have been: World, origonal, 50mm cavity, breather membrane, OSB, Studs with interstitial kingspan, kingspan over, VCL, batten/service voice, plasterboard. The sockets would then not have punctured the VCL, and the place would effecively be a timber frame made of sealed, draghtfree panels, stood up and joined together. The roof insulation would have joined up with the wall panels

Still, a good compromise is achievable; seal up the exterior against draughts as best you can too, repair pointing, fill obvious holes with expanding foam etc