We have some strange effects in our property…

[garym999]

• Most noticeable in the summer where the house can be relatively cool during a hot summers day but then at night the heat seems build up to become uncomfortable
• Black marking on carpet edges, presumably where air flows around carpet edges to skirting boards
• Noise travels between floors readily
• Lots of airflow within dot and dab drywall, behind sockets etc.
  
• Drywalls are open to loft
• Anything involving Artex is giving up, taping, coving etc. I thought it was because when the house was built it was in winter so did not dry off properly but I’m beginning to think it is down to damp airflow?

From the loft I have access to the building perimeter and top of wall cavity so could install cavity socks and foam fill the top of the drywall void.

• House built 1999/2000
• Insulated cavity wall with weep vents at first floor level
• Open cavity end to loft space
  
• Pretty sure there are no cavity closures around any of the windows
• Pretty sure floor joists are supported through the internal cavity wall so will have dried out and shrunk creating air paths

Without major renovation is there anything that can be done about any of the above and is it worth it? We have lived in it all this time afterall.

What has got me thinking about it all has been researching a potential garden office and the various build techniques.

TIA.

 

[Doggit]

Being hot in the summers getting pretty normal, and it'll be hotter in the upper rooms as heat rises.
The black marks would get dealt with ny thicker underlay, and better fitted carpets.
You can lift about every 6th floorboard, and cut and pack 170mm rockwool insulation under the floorboard. And if you've got long arms, you might only have to lift every 8th one.
You'd need to seal behind the plasterboard; drill holes every 6 inches at the bottom and the top, and slowly pump in some expanding foam, and that should spread sideways. Top and bottom of the wall of course.
If you've got damp airflow, do you have sufficient heating and ventilation.
I'm not sure about closing the cavities at the top, because if you are in a damp wet area, you may need them open to dry off the outer wall.
You should have cavity closers around the windows, but are you prepared to remove them to fit these in. Any foam you pimp in will just drop to the bottom.
Are you prepared to lift the floorboards, and foam around the joist ends.

 

[garym999]

Doggit, thanks for the prompt response.

The summer heat thing is odd in that by day the house is generally OK but them warms up after the sun sets, like a storage heater.

I can access the loft anytime and I had already thought of drilling and sealing the drywalls with foam but did not think about the bottom.

I guess I could drill a large hole to check a sample window. Sealing around the joists would be the biggest issue

 

[John D v2.0]

Sounds like you suspect you have "thermal bypass" i.e air blowing around the insulation layer.
Theoretically there's no problem having an air path behind the plasterboard, but you do need to have your insulation against your air barrier. Then the area behind the plasterboard would simply be part of your heated space. Dirty draught stains by the skirtings suggests otherwise though. Depending on the cavity insulation, the airtight layer could be a parge coat on the masonry wall before the plasterboard, a membrane if timber frame, or just a continuous layer of adhesive at the top and bottom of the wall where the plasterboard is dabbed on.
Your cavity in a modern house is part of the insulating envelope, as is the outside leaf. So all air bricks to underfloor voids should be sleeved through, and cavities should be closed (hopefully with insulated closers) on all reveals and at the top. Any penetrations for pipes etc should also be closed. The cavity should still be drained, but the weep vents are more like trickle vents so deemed not significant.
Depending on the type of insulation, by stopping up the draughts at plasterboard level, if the actual insulation has been bypassed, you might end up with condensation.
However as doggit correctly says, if you can stop too much air movement through to the room by remedial sealing at the plasterboard (and check for openings escpeically behind kitchen cabinets) then you then only have to worry whether air is blowing into the wall buildup from outside and then leaving again after cooling your wall.

 

[Doggit]

On reflection, if you put the rockwool under the floorboards, it'll warm the rooms up, cut the noise down, and reduce the need to seal the joist ends.

 

[garym999]

Not the most riviting pictures but they show the cavity wall make up & junction to the roof plate.

I have read that cavity closures to the top of the walls are now fitted primarily to stop fire progression but also help keep the cavity warmer but at the time of construction they would be open like now. I'm planning to make a test hole or two around a window later but guessing there is no closure around. If that is the case, not the best option but not too destructive, could I drill small holes around the inside perimiter of the window opening and seal with foam? It would seal the plasterboard cavity making the plasterboard around the inside of the frame the closure

I know, after some prodding, that the plasterboard void to the roof support timber is open. Cos the insulation is old now and cos it is not fitted that well against the edge the top of the plasterboard is basically open to the outside. The insulation is old now and cos it is not fitted that well against the edge the top of the plaster board is basically open to the outside. Doggits suggestion of using PU foam from inside would seal that gap before the roof support joist.

Note the addition of the bubble foil has been added by me previously, just to keep the worst of the damp and temperature extremes from the typical junk stored in a loft. What I did not understand at the time is that it would be better pushed down past the roof support joist.

 

[garyo]

Insulated cavity wall with weep vents at first floor level

What kind of insulation is in the cavity? Partial fill PIR board, or full-fill rockwool? If the former then I'd be more motivated to find and tackle thermal bypass issues in the cavity than the latter. Then you can concentrate on the bypass associated with the poorly fitted dot-and-dab.

 

[John D v2.0]

Doggits suggestion of using PU foam from inside would seal that gap before the roof support joist.

Good idea, make sure you use a foam gun rather than the hand held ones, as they are basically uncontrollable. At present your heated air gets behind the plasterboard and straight into the loft.

 

[John D v2.0]

What kind of insulation is in the cavity? Partial fill PIR board, or full-fill rockwool?

Looks like wool from the photos a and labelling

 

[garym999]

You can see where some of my crimbo break is going...

Yep the wall cavity contains wool slabs.

And second the use of a gun. Just been looking at them cos as you say, the plain cans just go everywhere. That place that fixes screws has one with a flexible hose attachement which may well help in less acessable areas.

As I have access all around the loft should I look at closing the cavity with socks while I seal the top of the plasterboard?

 

[John D v2.0]

Closing the cavity is less important if you have full fill insulation as the air can't blow throughout the cavity. However that insulation isn't and air barrier so it will still help reduce bulk air flow through the insulation.
If it's that easy go for it, but I wouldn't worry overly.
Others may have different opinions

 

[garyo]

That place that fixes screws has one with a flexible hose attachement which may well help in less acessable areas.

I've experimented with a 1 metre length of 8mm I/D flexible tube on the end of my gun-grade foam applicator. This pipe was gaffer taped to a couple of tent pole so that I could get it into places that the gun was too big to go.

Result: It works, but it's incredibly laggy. A squirt from the gun will take five seconds to fill the pipe and start coming out of the end. Then, as you keep the trigger pressed all is good. When you close the trigger, you have the reverse lag, plus the foam in the pipe continues to expand and will take 30 seconds to reduce to a dribble. So it works, but it's not going to be your best day at the office...

 

[garym999]

So the while the cat is away the mice play (yep the better half is out)...

I thought I'd see what coverage you get with the foam. So I built a little test cavity with a 15mm void which is what the dot and dab works out at. The lower foam was injected from the rear via a 10mm hole with a 3 second burst and the upper 3 second squirt was from above the open cavity as it will be when I manage to tackle ceiling/loft junction. I used fire/accoustic rated foam with a gun. First time I have used one and so much better than the normal cans because of the better control. The final foam picture is after an hour.

The dirty carpet edge is seen in the attached picture. This is an internal wall. Taking the skirting board off reveals the gap and provides a draft. Using foam I filled the gap between the floorboards and wall and also the plasterbaord and the wall. Initially I cut back the foam with a pad saw but this just seemed to hack it to pieces so in the end I used the buzz saw which did a much better job.

Hopefully I'll get to tackle the outside walls tomorrow and then I'll be able to judge if it has made any difference to the sound transmission from the lounge below.

 

[John D v2.0]

Nice work!! I love it when people do actual testing on things like that

 

[garym999]

Tackled one of the outer walls today. Was going to seal the ceiling from the loft. I started but access was a real b**ch. Also makes me think that fitting cavity socks to the top of the wall cavity might also be a no go although because the sock is flexible and I would not need tooling i might still be able to fit them. What impact would these have?

As the coving is coming off in places I will probably take it all down and pilot drill and fill before the new stuff goes back up to seal the top of the wall. Is the lightweight coving any good?

At the base it seems to have much larger gaps with some good 1/2"+ gaps between the floorboards and the walls let alone the plasterboard starting 1.5" up the wall. expains the draft and noise transmission. Added to which the skirting boards were not mounted flush with the floor but had a 1/4" gap for some reason.

The skirting will have to be replaced but at least the room is getting sealed. The lounge underneath also needs redecorating so I might take the ceiling down and insulate from underneath as all the taping and artex is shot.