Hi guys im looking for a bit of advice on flat roof construction.
Im building a 6m x 6.1m flat roof bedroom extension on the back of my house using a warm deck so my intention is this.
Im dropping an rsj half way through so as to split the span of my joists to around 3m lengths.
space joists at 400mm centres
lay firring strips 75mm-0mm
board out with a 9mm shutterung ply
lay a suitable vapour barrier on top of ply (sugestions on this welcome)
insulate with 150mm kingspan
ply board on top of insulation then either firestone rubber or 3 layer felt it.
I would like to use firestone rubber as in my opinion it will stay waterproof a lot longer than felt HOWEVER
Having been to look at various firestone rubber jobs initially it looks great but after time it starts to look a bit like a patchwork quilt with the shape of the boards underneath showing through etc and as its directly under our bedroom window i dont really want to be seeing that.
With 3 layer felt although im told it doesnt usually last as long it does at least look more pleasing to the eye over time.
Can i get round this by using a tongue and groove osb3 boards then hopefully i would lose the patchwork quilt effect and use the firestone rubber.
Also due to the depth of the roof deck 2 x 9mm ply + 300mm joist + 150mm insulation + roof covering = A deep unsightly fascia board which i am hoping to reduce by ending my joists which will be sat on a 75mm bedded wallplate at the cavity side of inner blockwork then continuing my brickwork 4 coarse to top of joist possibly somethig detailed like dental toothing corbelled out 25mm - 50mm then reducing my fascia to around 175mm
does this sound do,able.
Also any advice on ventilation of the joist cavity is welcome although im told i dont need this with a warm deck i do however intend to insulate the joist cavity with loft insulation.
ceiling plasterboard will be foil backed and i will be strapping down the wallplate every 2m.
any suggestions are welcome
Im building a 6m x 6.1m flat roof bedroom extension on the back of my house using a warm deck so my intention is this.
Im dropping an rsj half way through so as to split the span of my joists to around 3m lengths.
space joists at 400mm centres
lay firring strips 75mm-0mm
board out with a 9mm shutterung ply
lay a suitable vapour barrier on top of ply (sugestions on this welcome)
insulate with 150mm kingspan
ply board on top of insulation then either firestone rubber or 3 layer felt it.
I would like to use firestone rubber as in my opinion it will stay waterproof a lot longer than felt HOWEVER
Having been to look at various firestone rubber jobs initially it looks great but after time it starts to look a bit like a patchwork quilt with the shape of the boards underneath showing through etc and as its directly under our bedroom window i dont really want to be seeing that.
With 3 layer felt although im told it doesnt usually last as long it does at least look more pleasing to the eye over time.
Can i get round this by using a tongue and groove osb3 boards then hopefully i would lose the patchwork quilt effect and use the firestone rubber.
Also due to the depth of the roof deck 2 x 9mm ply + 300mm joist + 150mm insulation + roof covering = A deep unsightly fascia board which i am hoping to reduce by ending my joists which will be sat on a 75mm bedded wallplate at the cavity side of inner blockwork then continuing my brickwork 4 coarse to top of joist possibly somethig detailed like dental toothing corbelled out 25mm - 50mm then reducing my fascia to around 175mm
does this sound do,able.
Also any advice on ventilation of the joist cavity is welcome although im told i dont need this with a warm deck i do however intend to insulate the joist cavity with loft insulation.
ceiling plasterboard will be foil backed and i will be strapping down the wallplate every 2m.
any suggestions are welcome