Airtightness question regarding insulated slabs

Biff02008

Hi guys,

I am a self builder and currently nearing first fix stage of the build. I have a question regarding the grey coat render that needs to be applied to the internal leaf of the external walls before application of the insulated slabs.

This is my first time to post here so any help is much appreciated????

Basically I got an energy spec completed by a qualified person before the build started. In relation to air-tighness and the thermal liners, it was specified that a "grey coat" render be required prior to the application of all Thermal liners from floor level to underside of precast concrete floors (prior to installation of false ceiling).

So ,my question relates to the grey coat render, first fix electrics and false ceiling installation. Which comes first??? ie.

Do i get the electrician to chase walls and complete first fix, then apply grey coat render and then install false ceiling? - This means the false ceiling is not in place for the electrician when he is first fixing?

Do I get the the electrician to chase the walls, then install false ceiling, then complete first fix electrics and then ally grey coat render and then apply insulated slabs? - This means false ceiling is in the way of plasterer. Does this mean problems for the air tightness?

Do I get the electrician to chase walls, then install false ceilings, complete first fix, then apply an airtight membrane to area where precast slabs sit on the walls, then just apply grey coat render to area below the false ceiling where the insulated slabs will be applied?

Or is there a different and more correct way to carry out the 3 tasks of first fix electrics, render for the walls and false ceiling installation?

Apologies if this seems like a silly question but the guy that carried out the initial spec is on holidays for a few weeks and I want to make sure that I take the right approach. Am hoping that someone with the knowledge can point me in the right direction?

Note: I am not going with MHRV and it will be normal ventilation so maybe airtightness is too strong a word, but basically I want to try and cut out all other ways for heat to escape and draughts to come in.

clint_eastman

Biff02008 wrote: »

. In relation to air-tighness and the thermal liners, it was specified that a "grey coat" render be required prior to the application of all Thermal liners from floor level to underside of precast concrete floors (prior to installation of false ceiling).

Hi, I can't help, but am simply interested in the grey coat render as I had not heard (or been told about) this application. Can you expand on what it is exactly, I presume just an extra level of seal, make, material, application method etc?

Biff02008

Hey Clint, basically the grey coat render is just a scratch coat on the interior of the external walls before application of the insulated slabs.

The guy that carried out the spec used the "grey coat" terminology

Sorry for any confusion!!

paddy236

You should do the 1st fix electrics first. All conduit must be chased into the walls. Try and minimise the number of sockets and switches on the external walls and put the fuseboard on an internal wall also.
Then scratchcoat all the walls.
Then seal around the windows and external doors with airtight sealer and tape. I used siga sicral sealer and their white tape but their are two other manufacturers you can use (moy isover and ?).
I'm not sure how to seal the walls to the precast concrete floor but I'm sure someone else will answer that one.
Then put on the insulated slabs. I had to use 27mm slabs around the reveals.
Then put up the false ceiling.

This is how I would/did do it, but I didn't have the false ceilings. There may be better ways so feel free to correct me.

Paddy

FergusD

Another variant on a theme.... Have a look at:

http://www.boards.ie/vbulletin/showthread.php?t=2055975167

Not using insulated slabs, but the theory is the same. I took the option in the third post, chase walls, scratch coat 4" below the ceiling, fit the ceiling, first fix, then will slab ceiling and plaster walls next.

Hope that helps,

Fergus.

clint_eastman

paddy236 wrote: »

Then put on the insulated slabs. I had to use 27mm slabs around the reveals.
Then put up the false ceiling.

This is how I would/did do it, but I didn't have the false ceilings. There may be better ways so feel free to correct me.

Paddy

I know you don't have the false ceiling but I thought the best way was to put in the ceiling grid, slab and then put up the insulated slabs....same upstairs without the grid of course.

Biff02008

Thanks for your help guys;

can I run this by you...it might be completely way off the mark but just want to get your opinion. Steps to follow;

1. Chase the walls and install conduit.

2. Install air tight membrane (SIGa ,Isover etc) on the junction between top of ground floor ceiling and botton of precast slab. So basically the membrane would be 6 inches or so down from the top of the external wall and run a few inches onto the underside of the precast slab.

2. Now hang the grid for the suspended ceiling (no slabs being hung yet). The grid will probably hang 3 inches down from underside of the precast slab. Also, the air tight membrane will now be running down the wall 3 inches under the suspended ceiling grid.

3. complete first fix electrics, and tape up/fix all holes which have been put in the membrane during first fix.

4. Now scratch coat all the walls. For the external walls, they would be scratchcoated up to where the suspended ceiling grid is. (ie. the 3 inches from suspended ceiling grid to underside of precast slab is not scratched. it only has the membrane). Also, the scratch coat would cover the part of the membrane which is on the external walls below the suspended ceiling grid.

5. Install all remaining air tight membranes (around windows etc) and get a door blower test done.

6. if all is well then slabbing can begin.

Do you think this would work and make the area airtight? I'm trying to get around the catch 22 in the easiest way possible.

Thanks again for your help.

Dg_

just wondering what is the advantage of the scratch coat before you slab it ? is it just to fill any joints in the blockwork?

me_right_one

Dg_ wrote: »

just wondering what is the advantage of the scratch coat before you slab it ? is it just to fill any joints in the blockwork?

Excatly. I feel like I'm completely missing the point reading all this. What ever happened to just firing the insulated slabs up against the blocks and baeting in a few mushroom fixings?

sinnerboy

me_right_one wrote: »

What ever happened to just firing the insulated slabs up against the blocks and baeting in a few mushroom fixings?

Air tightness testing . It has shown that scratch coating tends towards significantly better results .

me_right_one

sinnerboy wrote: »

Air tightness testing . It has shown that scratch coating tends towards significantly better results .

And what about the skimcoat that will be going over the slabs? Does that not provide enough airtightness? What about flues and fireplaces, vents, when you open the back door? Surely this is just building regulations gone mad?

sinnerboy

me_right_one wrote: »

Surely this is just building regulations gone mad?

A common enough lament .




You would not be included on my tender list

sydthebeat

me_right_one wrote: »

And what about the skimcoat that will be going over the slabs? Does that not provide enough airtightness? What about flues and fireplaces, vents, when you open the back door? Surely this is just building regulations gone mad?

its not the surface thats the issue.,..... its all the holes that are put into it!!!