mr-gobby

The rafters can be 150mm based on span tables and architects spec as supplied for same extension few doors down . Carpenter is quite belts and braces and so priced for 200mm to avoid any possibility of sag later, he's done a few jobs I know of and has a very good reputation. It's having a couple large velux rooflight installed either side (size UK04) It's only got a 17.5 degree pitch, overall 5850 wide so internally 5250. I had a truss company quote, price was great but at the span the tie couldn't be high enough to give us the vaulted effect we want. Yes you can insulate under rafters and is likely option it was just a bug bear that a flat warm roof only needs 120mm but an inbetween rafter roof needs a lot more. The steel ridge is 178x102 so not huge, I have it on site now and we installed pad stone in house wall today.

Yes read some specify about 25mm gap into which you sag the breathable membrane, I figure it's a cold bridging of the rafter thing rather than insulation thickness. There are quilts which are insulative and act as a breathable vapour barrier to go on top and batten over thats thin enough not to need counter battening but it's quite expensive, in rolls of 1.5x10m a few brands think kingspan do one, superfoil is it? Makes a warm roof as opposed to insulated PB making a cold roof and loosing some albeit small amount of headroom (vaulted ceiling so just issue at lowest point really. Not got much to play with above though as ridge and flashing is close to a window corner. Thanks for replying Temp.

I'm at plate height and considering roof specification. No architect as such, drew plans ourselves but effectively copied similar extension nearby and have calculations for steel ridge and steel across bi-fold opening. I agreed with building inspector to provide details at each stage which so far has been fine. We have building width of 5.25m width 17.5 pitch and is 5.7m long. Two velux will go in, one either side. Glass area calcs are okay. My architect friend (who specified the one nearby) said 150mm rafters at 600 spacing was fine and complies from tables for building regs, I'd decided on 400 centres and the carpenter I'm using suggested that in his opinion 200cm joists would mean no chance of any sag later and also take adequate insulation if I used a breathable membrane for regs. Friend has just installed a flat warm roof and used 120mm celotex which passed inspection. When I mentioned 120mm for in between my joists the inspector said I'd need much more and that it was common to insulate under the rafters as well. Bit confused as to why if a flat roof can pass with 120mm I need so much more. Okay so the timbers are insulated above in that situation but really? I thought timber was thermally quite good anyway. Can it be done within a 200mm rafter? Anyone had similar experiences or can shed any light Thanks

May depend how deep are you pouring the concrete and thickness of mesh I suppose, I poured footings to 380/375mm off damp, pulled oversite off a touch below that to 400mm and allowed 100mm oversite, 10mm blinding, 100mm slab,.100mm celotex /insulation, 75 screed so I could just up the insulation with some 75mm XPS under the celotex on top of the sand blinding. Could put mesh down and space pipe off that rather than use mesh men. Pex al HDPE or pex al pex is another thing. I was looking at theunderfloorheatingstore.com and they list the pex al hdpe. I've put this extension on back of house but have also added 5mx3m to back of garage/workshop which is detached by about 30cm. Going to sink ufh pipe in that too while I'm at it but can't decide whether to use separate manifold for it and run flow & returns to it from house (quite a way from boiler, maybe 10-12m) or run the ufh pipes back to a manifold in the house along with the extension ufh pipework. Decisions decisions!

I was of the thinking of the mesh could be raised into the slab with meshmen but it makes navigating the mesh tricky

What ufh system you using Albert and more interestingly what pipe, there seems to be a few options. My concern is damage or rather avoiding it on installing the concrete. I've seen mesh on little upstands to raise the pipe height in the slab but not sure how the size 10's are going to navigate it all on pouring the concrete which maybe barrowed in my case. Interested as have 30m to do (okay bit less than you) and contemplating going into concrete slab to save on costs of into a screed (quotes are around £1000) . Ours is a single storey extension 6x6m externals and I may have some levelling issues adjoining the existing floor of our 1950's house but think I could overcome that for less than the cost of installing a screed. Just had brickies in to build up to damp yesterday, next bit is down to me to sort out before they return to build the shell. I've a couple things to address too including door thresholds and may have to nip out some inner skin bricks and backfill the cavity where the doors are going, I just needed them to get it built up to damp which they have done quickly and professionally.

Joining the forum in the hope of finding the answers even before asking the questions and thus hoping to avoid any mistakes! 6x6m single storey rear extension, brick front & block sides (hidden by garage and boundary fence), 3.6m 3 panel glass bi folding doors, vaulted ceiling/roof with velux or two, about 20 degree pitch. PD build been applied and cleared then after thought was I'd add 3x5m to end of detached (but adjoined) garage, it;s brick & pebble dashed but doing the add on in self made timber frame. Doing some work myself though I'm no brickie so that will get outsourced as I don't want to look at it and shake my head every time I look. Poured footings two days ago using Volumetric lorry and line pump, Went 375mm off damp (allowing block and two bricks) on house and 185 off damp on garage (flat block & a brick) they are both 50's build and wont have DPM's. Have sewer running through so dug metre wide pits either side about metre deep (from ground) went below the pipe either side but not under it. We needed build over agreement (done online) and shuttered that off before pour. Next phase is pull off oversite and dig a soakaway and it's drainage runs before digger and dumper can leave site. Then block & brick up to damp, hardcore and blinding, knock a bit of old kitchen down and break out its old slab before pouring new slab all over. Going to do wet UFH in screed, so insulate on top of concrete slab then install it myself onto that (recommends for wet systems/suppliers welcomed) it's south facing and we work from home all day, could insulate under slab and install into concrete and omit screed part but if it goes wrong its a hard dig out of the concrete and being south facing I don't really need the heat retention of a slab as in Summer it's hot enough. The garage timber frame will be single skin build to specification which would pass regs if we later convert garage so have insulation in slab too and walls probably 150 studwork insulated within, osb clad and breathable sheet with battens and some form of weatherproof cladding, not timber. (Any advice welcome on insulation and cladding) Think that sums up where I am. Regards Mark