Win the Vapour Barrier War for your Attic extension, Lofts, House Extension and Renovations

For new builds…the benefits of vapour barrier are proven. My gripes are about how it’s almost impossible to get these benefits for existing renovations because the structure, outer cladding and membrane is always already in place, and that no one seems to be pointing this out.
Having the structure walls and ceilings already in place makes installing a vapour barrier effectively very difficult.
This video shows the simple steps I take to get around this problem, and how I eliminate the risk of of vapour leaks turning into condensation for my attic extensions, loft insulation upgrades, house extensions and renovations.
#houseextension #atticinsulation #loft

[@plummetplum]

Hi Jeremy, will you do a video on installing the lead on a dormer tiled construction and aluminium soakers round a window. That would be great 😊

[@rogerwhiteley606]

Thank you for the very helpful introduction, I'm in the process of renovating a timber framed house from the 1980's.
The general construction principle seems to be a ventilated living space (ceiling level vents through the outer walls, vents in the window frames and vents in the floor space) with a vapour barrier in the ceiling but no barrier in the walls (50mm glass fibre, 12mm marine ply, outer tropical hardwood T+G cladding). They got that wrong - there are more roof level vents than floor level, so there's no chance of creating a proper updraft, especially if doors were closed, and of course the barrier had plenty of perforations for cables and light fittings.
It has been 'renovated' in the past, which consisted of adding what a pitched roof (which appears to be unventilated) over a flat root - which is probably bitumen roofing felt (I've not cut through the aluminium sheet below the felt, YET!). The void below the aluminium sheet was filled with 150mm glass fibre insulation and this void was unventilated, although somehow there had been a rodent infestation (mice, judging from the droppings, not recent) in at least part of this space. The ceiling was 12mm plasterboard with an aluminium vapour barrier on the top face and a nice coating of Artex on the ceiling surface (professionally tested and being handled appropriately based on the contents found).
On the basis that the flat roof is unventilated I propose to treat it as a 'warm roof', reinstalling PIR insulation, probably 100mm between the rafters and taping all the joints along the bottom face of the joists. I intend to leave a void below the aluminium panel although its impossible to ventilate along the 'eaves'. The new ceiling will be installed on battens leaving a space below the insulation for cabling and luminaires installed into the ceiling material.
I intend to replace the wall insulation with PIR, then a layer of breathable membrane, then horizontal battening, creating a wall void for installation of services, then the wall surface material.
All the windows are being replaced with new units, all with trickle ventilation. I'm also intending to install a positive input ventilation system, drawing air from the loft space.
In your opinion, does this sound like a sound approach?

[@build-better-things]

Hi. For a warm roof, you cannot put insulation between the rafters. Insulation needs to sit over the rafters/joists for a warm roof. And you definitely cannot have any unventilated voids, especially above the insulation. It’s hard for me to be precise with your questions without seeing a sketch.

[@rogerwhiteley606]

Thank you for getting back to me, the structure has been modified by the addition of a pitched roof [not yet investigated], the framing I called rafters are the horizontal beams supporting the original roof - each void has an small vent at the ends - about 60mm x 20mm - without any form of insect barrier, so the roof had a lot of empty wasps nests in it. Each void above the ceiling was completely filled with insulation, preventing any air movement from side to side. I will draw up a sketch and post it somewhere, I think the original roof could easily be turned into a warm roof by sealing the vents, but at the very least we have insect mesh to fit. We could fit PIR insulation leaving a gap above, permitting ventilation across the voids. The beams are a minimum of 200mm high, even allowing for the firrings.@@build-better-things

[@JamesGarwood]

Thank you for the great video!

[@build-better-things]

Thanks for the comment.

[@plummetplum]

For my loft design I'm so set on having a warm roof i am going to lower the ceilings. Theres just too many issues with cold roofs.

[@build-better-things]

Agree about warm roof if it’s possible. Let me know if you’ve any questions and good luck with it.