Fixing heat loss in my plasterboard tent

[gilesm]

Hello everyone.  Recently joined the board, but have been a lurker for a while!

 

A couple of years ago we moved into a 10-year-old timber-frame house with GSHP.  Brick outer & slate roof.  All well and good, except there is a significant heat loss problem.  We're living in a "plasterboard tent" and hope you can help me with some ideas??  Lots of detail below.

 

I've had a look through some of the holes behind sockets etc, and I can see that on the sloping roof areas, Celotex-style insulation is fitted between the rafters but some of the sections (circa 24x18" perhaps?) have tipped in & down, allowing air through.  There is a wind blowing behind the plasterboard (obvious without smoke pen).  The GSHP is working efficiently I believe, but the UFH simply cannot cope with the heat loss and we cannot keep rooms consistently above 20C when it's zero outside.  Bills are of course rather higher than expected, though we are on the Wiltshire/Dorset border so fairly mild.

 

Rooms upstairs have sloping ceilings down to about 3ft high, when the plasterboard becomes vertical.  So each top-floor room has a wind tunnel along-side it, within the thermal envelope.

 

I've bought a FLIR C3 thermal camera and have found 3 cold patches in one room's sloping ceiling. Checked with a borehole camera, saw the fallen insulation, and squirted in plenty of low-expansion foam.  This fixed the local problem there, but there are clearly more gaps which are not close to the plasterboard so the thermal camera can't easily spot it.  I assume/hope the problem is only with slipped insulation on the sloping roof and that there are a reasonably small number of failures, which will not increase in time.

 

But this targeted approach only works for the holes in the insulation which I can see.   I've put smoke bombs into the area within the insulation to hopefully see gaps around slates, but the smoke egresses over a large area of the slates.  Presumably due to intact fabric between slate and insulation.

 

How to fix this?  One intense approach would be to remove all of the tiles (attached with wire hooks, so do-able) and look for problems; or to remove chunks of plasterboard inside and go hunting with the thermal camera.   Any other thoughts on techniques to find and fix the gaps?  Is there some sort of blown insulation to fill up all of the eaves within the thermal envelope??

[scottishjohn]

how about icyene foam pumped into the walls --it was the solution suggested to me for a similar house --

they cannot fill the outer cavity in a brick /wood frame house -cos they might trap moisture then wood frame   rots away  

but totally possible to just make small holes in plasterboard  between vertical studs and  or so and fill up all space behind your plaster board  -should make it air tight and lift the insulation in one go 

just a small bit of decorating to do after.

not sure blown cellulose will make it air tight --could be wrong 

 

Edited February 14, 2020 by scottishjohn

[Cpd]

It’s a really tricky situation because the fact that the insulation has fallen down indicates that ALL the insulation is loosely fitted.  air will happily bypass ALL the insulation if there is a few mm gaps that you miss,   so it’s not a solution to just poke the fallen ones back. One solution is to get serious and  strip all the plasterboard out and then deal with the insulation by foaming it all in and consider adding extra or as @scottishjohn says getting it topped up with spray foam and then a VCL and then re plasterboard. Sounds like a lot of work but I think you will be forever chasing your tail if you don’t hit this problem with a big stick. 

[ProDave]

There is no "easy" solution that I know.  It is indeed a common problem, and boils down to lack of care by the builders.  As an electrician, it is oh so common on a windy day to remove a switch or socket and be greeted with a howling icy gale coming out of the hole.  This is true of the new build I am working on at the moment!!!

 

My solution would be convert the room in roof section to a warm roof.  This means the insulation would follow the roof line right down to the walls, so the triangle "coombe" section would be entirely within the heated envelope of the house.  That makes it a LOT easier to detail.  the bad news is I can't see a way to do that without completely stripping off all the plasterboard from the roof sections, sorting out the insulation, and re boarding.  Anyone have any better ideas?

 

[Declan52]

So it's either remove the plasterboard and upgrade and fix what's between the joists. Pretty messy work.

Or put another layer of insulated plasterboard over what you already have. 

How much head room so you have to the ceiling. Could you afford to loose 65mm for a 50mm insulation backed sheet of PB or 115mm for a 100mm backed sheet.

Have you got access to the wind tunnels at each side??

[scottishjohn]

OR

 get it pumped with foam then add vcl on top of exsisting plasterbord -the fit another layer of plasterboard ?

 less mess that way and could be done without wrecking house while you are doing it

[ProDave]

41 minutes ago, scottishjohn said:

OR

 get it pumped with foam then add vcl on top of exsisting plasterbord -the fit another layer of plasterboard ?

 less mess that way and could be done without wrecking house while you are doing it

The trouble with that, is you are supposed to maintain an air path between the eaves coombe and the ridge space to ventilate a cold roof.  Done properly, the insulation will be touching the plasterboard and secure, leaving the ventilation gap between the insulation and roofing felt

[scottishjohn]

14 minutes ago, ProDave said:

The trouble with that, is you are supposed to maintain an air path between the eaves coombe and the ridge space to ventilate a cold roof.  Done properly, the insulation will be touching the plasterboard and secure, leaving the ventilation gap between the insulation and roofing felt

not arguing --but we don,t know what type of roof it is at this stage ,or if it is cold roof type 

I,m guessing as he has insulation shoved up between rafters is not a true cold roof design anyway

we don,t even know if it has sarking boards+ conter batons  or drapped vcl type and single batons  --as in england 

needs some more detailed surveying before commiting to any solution  

[Ferdinand]

Have you taken a set of photos from the outside while it is cold to look for warm spots, which may show up some of the ones you cannot find from the inside by looking for "cold"?

 

Ferdinand

 

Edited February 14, 2020 by Ferdinand

[gilesm]

Thanks for the great replies!

 

Ferdinand: yes, I have taken thermal photographs from the outside during a recent cold, still day.  No significant heat patches from the vertical brickwork, but there are some obvious patches on the sloping slate roof.  Hence my assumption those are the areas to focus on.  

 

Scottishjohn, I think we have a "cold roof".  I have the construction drawings, and have tried to sketch out the roof structure, attached.  I assume there's a vapour barrier somewhere but I'm not sure where.  There is some heavy transparent plastic sheet right behind the plasterboard in our upstairs laundry room, but maybe that's just for the laundry area.  [Edit to add: this is probably the vapour control layer?]

 

ProDave, the triangle "combe" section is within the insulated area, as the diagram should show.  There are plenty of cables and the UFH pipes going through it (see picture, looking horizontally outwards through a small hole from first floor laundry, at vertical insulation before the roof slope starts).  From what you and the others say, I could pump spray foam or cellulose/alternative into this area through holes in the plasterboard.  Any future wire/pipe repairs would be hampered, but it would (I think) fix the draught problem.  I don't think this would affect ventilation, as it would all be within the insulation envelope?

Edited February 14, 2020 by gilesm

[ProDave]

@gilesm if the insulation has been done like that in your sketch, then it looks like it has been done as a warm roof. But if that is the case, the loft and eaves void should NOT be ventilated.  And the air tightness layer should be adjacent to the insulation.

 

I would start by cutting an access trap into the void sections so you can crawl in there and have a proper look at how it has been done, and see of you can see where the problems are and hope you can get at them to fix it.

 

 

[gilesm]

On 14/02/2020 at 22:20, ProDave said:

@gilesm if the insulation has been done like that in your sketch, then it looks like it has been done as a warm roof. But if that is the case, the loft and eaves void should NOT be ventilated.  And the air tightness layer should be adjacent to the insulation.

 

I would start by cutting an access trap into the void sections so you can crawl in there and have a proper look at how it has been done, and see of you can see where the problems are and hope you can get at them to fix it.

Thank you ProDave.  From reading up some more about warm/cold roof construction on https://www.designingbuildings.co.uk/wiki/Warm_roof then yes it looks like a warm roof.  The insulation is in line with the rafters, and the space between ceiling/rafters should be warm (and not ventilated to the outside).  I don't yet know where the air tightness layer is supposed to be.

 

My plan of attack now is to put in a loft access hatch to get into the roofspace (there's up to 5ft of headroom so should be easy to look around more thoroughly).  The joists are circa 14" apart and there are two layers, so I'll get our friendly builder to do it!  Will report back when I know more.  Thanks for the help so far...