Hi guys
ive built my extension to roof level which will be a flat warm roof design.
100mm brick outer leaf, 100mm cavity drithetm 32 full filled, 100mm aerated block internal leaf.
Joists rest on 100mm internal wall leaf and innerleaf blockwork continues between joists and above.
External brick skin to same height as internal leaf so as to envelope joists and insulation inside of build.
9mm wbp board fixed to top of joists.
Vapour barrier.
130mm celotex slabs to 9mm wbp board.
18mm t&g osb3 on top of celotex.
waterproof membrane (grp proposed) to finish.
Question 1. Initially I envisaged celotex to fit flush within the internal aerated blockwork top inner edge build and osb to go across top of Insulation and over inner and outer cavity skins. Would this give me a significant cold bridge where osb rests on the themal blocks and also causing possible condensation problems with a dewpoint?
Question 2. Would it be better to lower internal blockwork so as to accomodate celotex to then go over the too of it and continue to inner face of outer leaf brickwork?
Question 3. Continuing with q2 proposal would it be best to end celotex on top of internal skin and butting with the cavity drytherm raised up to the celotex top edge?
BC had advised not to place celotex next to inside of external wall unless either leaving a 25mm gap or adding a dpm between.
Im worried leaving a 25mm gap would allow a void for interstital condensation?
He also advised I wouldnt need a vapour membrane at warm side of ceiling under the celotex which really has confused me.
Im happy ending the celotex on top of internal blockwork where it will be in butting junction with the drytherm cavity insulation just wondering if they will interact negativley regards condensation?
Any advise will be appreciated so I can get this roof finished hopefully before christmas to keep her indoors happy!
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ive built my extension to roof level which will be a flat warm roof design.
100mm brick outer leaf, 100mm cavity drithetm 32 full filled, 100mm aerated block internal leaf.
Joists rest on 100mm internal wall leaf and innerleaf blockwork continues between joists and above.
External brick skin to same height as internal leaf so as to envelope joists and insulation inside of build.
9mm wbp board fixed to top of joists.
Vapour barrier.
130mm celotex slabs to 9mm wbp board.
18mm t&g osb3 on top of celotex.
waterproof membrane (grp proposed) to finish.
Question 1. Initially I envisaged celotex to fit flush within the internal aerated blockwork top inner edge build and osb to go across top of Insulation and over inner and outer cavity skins. Would this give me a significant cold bridge where osb rests on the themal blocks and also causing possible condensation problems with a dewpoint?
Question 2. Would it be better to lower internal blockwork so as to accomodate celotex to then go over the too of it and continue to inner face of outer leaf brickwork?
Question 3. Continuing with q2 proposal would it be best to end celotex on top of internal skin and butting with the cavity drytherm raised up to the celotex top edge?
BC had advised not to place celotex next to inside of external wall unless either leaving a 25mm gap or adding a dpm between.
Im worried leaving a 25mm gap would allow a void for interstital condensation?
He also advised I wouldnt need a vapour membrane at warm side of ceiling under the celotex which really has confused me.
Im happy ending the celotex on top of internal blockwork where it will be in butting junction with the drytherm cavity insulation just wondering if they will interact negativley regards condensation?
Any advise will be appreciated so I can get this roof finished hopefully before christmas to keep her indoors happy!
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