best to have a well insulated but well ventilated loft.

I think foam might be best in your cavities as it will be the most air tight choice to stop draughts whipping away your heat.

Love the idea of EWI, I would use eps if it were mine

all power to your elbow.

Posted By: tbhulseI am upgrading the loft insulation too - should I be closing the cavity at the top and how? Am concerned about air tightness in the loft - any ideas on improving this other than a big can of spray foam? Any other comments appreciated.

I would take off any soffit boards & carry the EWI over the top of the wall closing the cavity.

The best way of making the ceiling below the loft airtight is to fit a layer of polyethylene to the existing ceiling, batten over it to create a service void for running electrical cables & fit a new ceiling to the battens. If this is not practical then you could fit polyethylene to the top side of the ceiling, but unless you have a simple purlin roof, its likely to require a lot of cutting & taping around ceiling joist hangers, etc.

David

The ideal is EWI to walls, continuous with similar EPS on OSB boarded over the top of the rafters, tiles/slates replaced but a bit higher up. The roof OSB is adequately airtight, without any problems with interruption by internal trusses etc. Unfortunately EWI can't be relied on to be airtight, so either an external rough-render (breatheable) on the brickwork before EWI-ing, or the internal plaster wd be your wall airtight barrier.That (like IWI) is problematic because of joist penetrations and joists so close parallel to wall that you can't make the internal plaster continuous through the floor thickness. Also needs connecting up with roof OSB (or with over-joist membrane if trying to air-tight at loft floor level).

Posted By: tbhulseLike the idea of carrying the EWI over the wall, as long as I can do that without blocking the airflow.

By that you mean airflow to underfloor? Not confusing with wall airtightness or water vapour breatheability. My approach is to dig a perimeter trench down to bottim of foundations, carry the EWI down into the ground as deep as feasible, backfill with Leca (lightweight expanded clay aggregate, little malteser balls, usefully insulative), optionally making a french drain out of it. Then the underfloor subsoil is kept warmish and bone dry (if french drain), so the underfloor void not liable to condensation, so you can block the air vents (which actually just import moisture) and you have a draught free fairly insulated ground floor without having to disturb it at all.

I just wondered if you had any update on the EWI + CWI? I'm thinking of doing the same and would be interested if you had worked out the U value you might achieve.

From my research so far and my very limited understanding, the remaining interior wall should still provide enough thermal mass. In fact one source mentioned that beyond a certain depth of wall (something like 10cm), there are greatly diminished returns on the thermal mass effect.

I'd not considered air bricks at all in this. What side-effects could there be of covering those with the EWI?

Posted By: eniacsIf doing EWI on a cavity walled house, make sure the cavitys are filled with somthing, otherwise they will have a negative effect on your toasty warm EWI coating!

Why so? (can guess, but just checking)

What if the airtight layer is outboard of the cavity, so it's not open to outside air?

I'm not so sure these days about recommending conc cav fill, unless converting the wall into a uni-directional thermal store as per http://www.greenbuildingforum.co.uk/forum114/comments.php?DiscussionID=9743&page=3#Item_12

Posted By: Swarmbeyond a certain depth of wall (something like 10cm), there are greatly diminished returns on the thermal mass effect

Don't ask me - it's a mystery! Perhaps what Swarm summed up, ST's ongoing back yard experiment, realisation that uni-directional mass storage works so clearly, hoping that simple 'in the room' massiveness would come equally clear, but it hasn't.

Mind you, if using a cavity wall as uni-directional storage (heat input from collectors into outer face of wall, traveling uni-directionally inward), then wd certainly conc fill it, plus think about adding more mass, wood fibre or Hempcrete as EWI perhaps. Or the cavity could be kept for an air-as-thermofluid system.

I still think the outer leaf is a mass asset that should be used, rather than thermally isolated and lost.

Loft insulation between and over joists total 300mm+ of insulation, easiest with quilt, leave no gaps, dont block the air path at the eves leave 25mm clear gap

I did a little sketch of what I think is correct for OSW and roof insulation. Please could you offer a critique?

Sorry, trying again....

Photo above finally.

Isnt board better for the roof? easier to maintain a vent gap?

In Europe 200mm of eps is common with thin coat hitgh tech render in a thin plastic mesh for EWI

Posted By: samuelvincentvellaNo comments on my sketch?

I cant seem to find any best tried and tested EWI system for a 1950s Cavity wall bungalow. Can anyone point me to a good thread/blog/info source please?

We have similar, see below

Posted By: samuelvincentvellaPhoto above finally.

Isnt board better for the roof? easier to maintain a vent gap?

That's what we have done, but we have done a loft conversion

''when friends have popes in''

Are popes more or less likely to feel the cold tan members of the general population? And anyway, I thought the nature of the beast was that you could only have one in at a time.