new extenstion wall thickness

Crimsonforce

Just looking for some confirmation that the below is OK for block work extension.

20mm exterior plaster, 100mm block, 40 mm free cavity, 60 mm insulation, 100 mm inner concrete block, 28mm insulated slab fixed to blockwork , skim or dryline finish.

floor will have 50 mm screen on 80 mm floor insulation with radon(dpm) under insulation

Thanks

Gumbo

Crimsonforce wrote: »

Just looking for some confirmation that the below is OK for block work extension.

20mm exterior plaster, 100mm block, 40 mm free cavity, 60 mm insulation, 100 mm inner concrete block, 28mm insulated slab fixed to blockwork , skim or dryline finish.

floor will have 50 mm screen on 80 mm floor insulation with radon(dpm) under insulation

Thanks

What did your engineer say?
The structural floor build up material is a structural item and this needs to comply with IS888 2016 (March update) so that's just the start.

Skin or dry line finishe and a 28mm insulated slab? Can you explain this detail?
I would deem it a little light on the insulation front tbh

Crimsonforce

engineer said it was ok, but looking for a someone who has gone through the process.

28mm slab ( insulated plasterboard) , skimmed...

Gumbo

Crimsonforce wrote: »

engineer said it was ok, but looking for a someone who has gone through the process.

28mm slab ( insulated plasterboard) , skimmed...

It's ok i suppose. I would rather a bigger cavity with full fill but depends on individual circumstances. I like to keep all the insulation in one plane but others may feel different n

sydthebeat

why would you use an insulated slab?

Gumbo

sydthebeat wrote: »

why would you use an insulated slab?

It's the go to detail in my experience Syd. 90% of my jobs in inspecting would have it.

sydthebeat

kceire wrote: »

It's the go to detail in my experience Syd. 90% of my jobs in inspecting would have it.

i think dublin is then probably 5 years behind the rest of the country.

its a bit strange as its not a space saver, as was typically used as the argument for the 'hollow block' build that became extremely popular in the dublin area... perhaps its just builders there thinking dry lining is a necessary thing.

makes no sense at all in a new build though

Crimsonforce

whats the alternative?

sydthebeat

make the cavity insulation board 15mm wider .....

not only are the savings are obviously significant, but the end product is a much better build.

you save on:
1. the big price difference between the extra 15mm of cavity board (probably €2.50 /m2) compared to the insulated slabs (€10 / m2)
2. the longer fixings for attaching rads, curtain rails, kitchen units etc and the risk of the sagging in the future.
3. the over sized window boards

the much better construction accounts for:
1. the easier to make air tight (no more draughts)
2. better thermal mass (walls retain heat better and regularizes the house temps meaning the help keep cooler in summer and warmer in winter)
3. doesnt hide dodgy slapped up blockwork (which i think is a big reason its suggested by builders)

Crimsonforce

thanks for that syd, very informative

so use something like Kooltherm K8 Cavity Board Partial fill cavity wall insulation and then 3
mm skim coated 12.5 mm plaster board?

sydthebeat

Crimsonforce wrote: »

thanks for that syd, very informative

so use something like Kooltherm K8 Cavity Board Partial fill cavity wall insulation and then 3
mm skim coated 12.5 mm plaster board?

no... dont use internal plasterboard, thats for timber studwork not blockwork.

put a gypsum base coat on the internal blockwork and then your gypsum finishing coat, thus creating a solid internal masonry leaf to achieve the thermal mass i described above.

Metric Tensor

kceire wrote: »

It's the go to detail in my experience Syd. 90% of my jobs in inspecting would have it.

I am really surprised by this - I thought that the majority of the industry had moved away from this for all the reasons syd mentioned.

1. Air-tightness wise it's a nightmare
2. Interstitial Condensation is always a risk.
3. Throwing away thermal mass

What air tightness methods are people using kceire? Are they plastering behind the slab? Membrane?

Calahonda52

OP, kc asked you in post two to clarify the detail, would help immensely if you did.

I don't think anyone is suggesting plasterboard only as a finish, especially if it is dabbed on to hide poor blockwork.

My guess its cheaper than the proper finish of sand cement plaster and then skim

A properly constructed and properly functioning insulated cavity is something that requires skill and attention to detail, which can be hard to find these days.

Crimsonforce

Calahonda52 wrote: »

OP, kc asked you in post two to clarify the detail, would help immensely if you did.

I don't think anyone is suggesting plasterboard only as a finish, especially if it is dabbed on to hide poor blockwork.

My guess its cheaper than the proper finish of sand cement plaster and then skim

A properly constructed and properly functioning insulated cavity is something that requires skill and attention to detail, which can be hard to find these days.

What part of his question did I not answer?

Gumbo

sydthebeat wrote: »

i think dublin is then probably 5 years behind the rest of the country.

its a bit strange as its not a space saver, as was typically used as the argument for the 'hollow block' build that became extremely popular in the dublin area... perhaps its just builders there thinking dry lining is a necessary thing.

makes no sense at all in a new build though

Metric Tensor wrote: »

I am really surprised by this - I thought that the majority of the industry had moved away from this for all the reasons syd mentioned.

1. Air-tightness wise it's a nightmare
2. Interstitial Condensation is always a risk.
3. Throwing away thermal mass

What air tightness methods are people using kceire? Are they plastering behind the slab? Membrane?

Ohh I agree. But as you guys know, all the sites I inspect are in private ownership and not detailed by myself so I can't say anything other than ask the question in why the detail was selected. Most just say it was handier, especially for extensions anyhow. And then they'll argue that the blocky was too expensive to lay 2 courses

Most new build houses in my area seem to be metal fixings, insulated between and then an insulated board over that.

Bullocks

sydthebeat wrote: »

no... dont use internal plasterboard, thats for timber studwork not blockwork.

put a gypsum base coat on the internal blockwork and then your gypsum finishing coat, thus creating a solid internal masonry leaf to achieve the thermal mass i described above.

Are many people using gypsum base coat on block work and what's the benefit of it over sand and cement ?

Crimsonforce

Bullocks wrote: »

Are many people using gypsum base coat on block work and what's the benefit of it over sand and cement ?

The use of Gyproc Floating Coat or Base Coat instead of the traditional sand and cement allows earlier application ofthe finish coat plaster.

sydthebeat

Bullocks wrote: »

Are many people using gypsum base coat on block work and what's the benefit of it over sand and cement ?

more flexible
no lime so no risk of paint spreading
quicker application of finishing coat

Metric Tensor

How do you find it for AT syd? We usually specify sand and cement - it'd be nice to have an alternative when necessary.

sydthebeat

Metric Tensor wrote: »

How do you find it for AT syd? We usually specify sand and cement - it'd be nice to have an alternative when necessary.

pretty much the same result for AT

i dont really have a personal preference either way, other then ensuring the "paint spreading" risk is negated

Calahonda52

Crimsonforce wrote: »

What part of his question did I not answer?

Skin or dry line finishe and a 28mm insulated slab? Can you explain this detail?

hexosan

Bullocks wrote: »

Are many people using gypsum base coat on block work and what's the benefit of it over sand and cement ?

My plasterers used it first time on my build and haven't went back to sand & cement. They swear by it and claim it makes they work a lot easier.