Room in roof and awkward wall insulation top up question

[Avendit]

Hi all,

 

I have a 1960's chalet style house that we have done a lot of work on so far.  As part of an extension, heatpump and new heating system install I had open cell sprayfoam added under the suspended timber floor (100mm) and around all the room in roof spaces (150mm between rafter) at roof height.  We have since then added 90mm of EPS EWI to most of the walls, and Solar PV.  We have also added MVHR to most of the house after Jeremy sung its praises on a different forum.

 

The EWI walls work out around U0.17, and the roof U0.24.

 

I have 2 areas I'd appreciate some advice on.

• The first is the roof.  It seems mad to have worse insulation on the top of the house, so I was looking for relatively easy DIY-able ways to improve this as much as possible.  I am only looking to do this in the main attic space - about 50% of the surface area.  There is no space to do anything in the angled celling areas of the room in roof (I could/will add insulated plasterboard when we next decorate, but its not a big area) and I can't get back into the eves without incurring the wrath of the decorator (also me btw). One suggestion I thought of was to use superfoil under the sprayfoam for this - its not cheap, but my DIY skills aren't amazing so having something I just unroll and staple in place then tape up would be very much preferred.  It would also conform around the imperfect spray foam surface and generally simplify things vs installing anything solid.  It also seems to be price competitive at the 45mm thick vs EPS.  
  • Talking to the manufacturer they were reasonably insistent on the vapour barrier version of the product, where I had selected the vapor open version so as not to mess with the current building.  And I can't see using a vapor closed version over half the roof height being smart?
  • Is taking half the roof from 0.24 to 0.15 and leaving the rest just a dumb idea?
  • if doing something is OK, is superfoil a decent approach in this case, and if so, vapour closed or open?  To be clear, having looked at it I wouldn't choose it for any other application.  It just seems bettered on all fronts by something else except here where I just need to unroll and staple.
  •  
• The second is a wall that was on the party line, so I couldn't add EWI - I don't think I could even render it legally speaking, that's how on the boundary it is.  Its a weird build up of 50mm insulated plasterboard, inner brick, 20mm cavity with 10mm EPS boards floating around, external brick.  I can't find any good solution for this.  My architect things that there is already a cycle of condensation and evaporation in the wall, and adding any internal insulation just makes this worse.  I can't add anything into the cavity, and even if I did 20mm wouldn't amount to sod all anyway.  Any smart ideas?  Currently guesstimate is U 0.42 over 25 m^2.

 

Thanks massively!

 

 

 

[Avendit]

Can I reasonably add anything up in the attic? If so, any suggestions for what?

[Avendit]

Well, have found the answer to at least the annoying wall today.

 

I took the skirting off today to inject a tin of spray foam so the wall is now actually joined to the floor (much improvement around the toes, well worth the effort!) and found I had the build up wrong.  I thought it was 

• Insulated plaster with 5cm bonded EPS
• brick
• 2cm cavity with 1cm of EPS in.
• brick
• render

The first layer turns out to be just normal plaster on a loose 3cm sheet of EPS.

 

So obvious answer is next time we are decorating, its plaster off, EPS out, PIR in and thick insulated plaster board on top.  With 10cm insulated board on top of 3cm of PIR I should get around 0.14, which brings that wall into line with the rest of the building.  Small condensation risk, so need to get a good vapour barrier in there somewhere, but choosing that is a problem for much later.

 

Just the question of the attic to go.  I still don't like the idea of a non-breathable barrier up there, given its all breathable just now.