Advice needed, considering Solid Wall Extension

Wonky Knees

I would appreciate any advice on this proposed extension.

The extension comes out from the back of the house like a box. The length is 10M the width is 9M. The front of the extension comprises of triple glazed windows in three sections, no windows or doors in either wall.

My main concern is ensuring that the construction is damp-proof and warm.

I'm thinking of using the quinn lite B5 215mm.
External render and skim (not sure which are best products for this block).
Internal: Batons/45mm with some form of insulation between the bats and then fix Q-term 60/12.5 with a further skim coat.

Alternative is to use some form of external waterproof insulation and then render over this and on the inside bat the walls, fill the gaps between bats and then fix a foil back board to the bats and plaster. But vapour and moisture may be an issue.

Self build headache!

muffler

Out of curiosity why have you ruled out a cavity wall?

sinnerboy

90m2 will require planning before you look for build specs - do have permission ?

Wonky Knees

Hi, yes have permission. Issues are cost, time to construct and internal space.

sinnerboy

Keep it simple !

215 QL + 60 PIR 40 airspace 100 QL + render

0.18 U value with near-as-damn-it tried and trusted familiar build technique

Just watch that QL are gently dampened before plastering - ( int + ext )

Wonky Knees

Thanks Sinnerboy, but I'm trying to avoid a cavity wall construction, unless the advice convinces me that a solid wall construction is a mistake.

Currahee01

You might have to use some form of cavity for ventilation. Have you considered a closed timber frame with cement board on the external face?

sinnerboy

fatimamansions wrote: »

Thanks Sinnerboy, but I'm trying to avoid a cavity wall construction, unless the advice convinces me that a solid wall construction is a mistake.

drylining leads to very difficult detailing when trying to archeive continuity of insulation

external wall insulation is expensive with only a few specialists in the market

sydthebeat

fatimamansions wrote: »

Thanks Sinnerboy, but I'm trying to avoid a cavity wall construction, unless the advice convinces me that a solid wall construction is a mistake.

as this new build is an extension, unless it is thermally broken from the main building, it will not be very efficient (assuming the existing build is old an not efficient).... hence the argument as to how viable a single leaf construction is, from am energy conservation point of view...

If you are externally insulating, then do not dry line internally, it can cause more problems than its worth. use solid quinnlite blocks internally and plaster to create your airtight layer.

If you are drylining internally, you seriously need to look at condensation risk problems. Solid block walls with non breathable insulations WILL cause condensation within the wall construction so you need to design a way that this condensation does not gather to cause mould.

The success of teh final result will depend on what renovations you are doing to teh existing to make it more energy efficient ie heating system and controls, upgrading insulations, improving air tightness...

Wonky Knees

Currahee01 wrote: »

You might have to use some form of cavity for ventilation. Have you considered a closed timber frame with cement board on the external face?

No, I haven't considered this. Thanks anyway.

Wonky Knees

sinnerboy wrote: »

drylining leads to very difficult detailing when trying to archeive continuity of insulation

external wall insulation is expensive with only a few specialists in the market

Are you saying this is a bad move and to consider a cavity using QL as an inner leaf?

Time is an issue: I estimate 300 blocks for each wall, and I'm hoping that two brickes can put up from footing in one week.

Wonky Knees

sydthebeat wrote: »

as this new build is an extension, unless it is thermally broken from the main building, it will not be very efficient (assuming the existing build is old an not efficient).... hence the argument as to how viable a single leaf construction is, from am energy conservation point of view...

If you are externally insulating, then do not dry line internally, it can cause more problems than its worth. use solid quinnlite blocks internally and plaster to create your airtight layer.

If you are drylining internally, you seriously need to look at condensation risk problems. Solid block walls with non breathable insulations WILL cause condensation within the wall construction so you need to design a way that this condensation does not gather to cause mould.

The success of teh final result will depend on what renovations you are doing to teh existing to make it more energy efficient ie heating system and controls, upgrading insulations, improving air tightness...

yes, the existing build is 1930. Thanks for advice on internal dl. The roof is almost flat. Zinc warm roof. Will vents solve the condensation issue? The windows in the rear are all going to be triple glaze. The front sash will be replaced for double glaze, the attic is also going to be converted and insulated and getting a condensing gas boiler and rads from megabad. I'm also going to overspec the ground slab.

sinnerboy

fatimamansions wrote: »

Are you saying this is a bad move and to consider a cavity using QL as an inner leaf?
.

Yes .

Spec as post 5

Wonky Knees

thought I should finish this discussion off. Some of the details I can't remember but basically the architect has designed the extension with cavity block. Some form of render on the outside. Internally he has horizontal bats with insulation followed by vertical bats (services) then plaster board and walls plastered. He mentioned something about an intelligent membrane with the insulation. Room will have vents with the option of having some sort of system installed in the attic which runs down through the house in the future which 'zaps' the moisture. Sorry for the infant-like response.

Mellor

fatimamansions wrote: »

thought I should finish this discussion off. Some of the details I can't remember but basically the architect has designed the extension with cavity block. Some form of render on the outside. Internally he has horizontal bats with insulation followed by vertical bats (services) then plaster board and walls plastered. He mentioned something about an intelligent membrane with the insulation. Room will have vents with the option of having some sort of system installed in the attic which runs down through the house in the future which 'zaps' the moisture. Sorry for the infant-like response.

I really don't like the idea of drylining an extension where the original house isn't drylined.
Cavity insul would of been my prefered choice here

onq

Mellor wrote: »

I really don't like the idea of drylining an extension where the original house isn't drylined.
Cavity insul would of been my prefered choice here

Is the original house insulated at all?

Does it have a cavity?

ONQ.

Wonky Knees

Not mad about it myself, but my ignorance of building has me saying 'OK' to the Architect's arguments - he tells me he did the same to his own house which is close by. I am very happy with the architect, he's a partner in a firm that has done a lot of work around town and he appears to love his work.

I have no idea about the original house. The extension is an ad on and there will be very little work done to the original house apart from two break through where windows currently exist and of course new windows all round. House built around 1930s (semi-D), red-brick front.

Will keep you posted.