Laying floor insulation and screed

Rossdarragh1

Hi,

Hoping for some help here. I'm due to start laying floor insulation tomorrow in preparation for screed.

It's a timber frame house with concrete sub floor and 62.5mm insulated slab on all perimeter walls. I'll be putting in 100mm insulation on the floor as there's already insulation within the sub floor so 100mm will suffice.

When slabbing the walls I left all slabs up 100mm from the subfloor with a view to sliding the floor insulation in underneath the slab. My question is, is there a need to place edge insulation on the base of to walls and let the screed run into it?

I presume there is no need as there is no cold bridging to be wary of as the screed will be running up against the insulated slab with no block wall being touched. Am I correct in thinking this?

Also when laying plastic over the floor insulation how far should I run it up the walls? I presume any tape can be used to seal joints in the plastic and tape it up the wall?

Also my tiler wants to screed the shower base himself with sand and cement but I presume it's still necessary to run the floor insulation into the shower?

I'll be putting in 50mm screed, alpha hemi-hydrate.

BryanF

I'd be buying some super tape to ensure not a drop of moisture is getting into the gyproc.

Where is your air-tightness layer?

Of course you insulate the bathroom.

What is the wall build-up?

Any chance you'd posted the floor junction detail?

You mention thermal bridging, how are you dealing with it at other junctions? For instance internal walls meeting external wall and ceiling junction?

Rossdarragh1

Is super tape a particular brand or do you just mean really strong tape?

The perimeter studs are foamed with my air tightness later behind the insulated slab.

I don't think there's an issue with thermal bridging elsewhere as all internal studwork is fixed to the timber frame and not touching the outer blockwork.

Not sure what you mean by wall build up to be honest?

Only have a basic pic of room but it won't let me post. Floor insulation will effectively be underneath the insulated slab , up against the timber anchor on which the timber frame is constructed. Screed will then run up against the insulated slab on perimeter walls and 12.5 on internal walls. Is it ok to allow screed run up against slab without edging. Presume the purpose of the edging is to prevent thermal bridging which to my knowledgr is not an issue for me.

BryanF

Cut back the plasterboard so it doesn't get soaked by the screed.

delfagio

What should be done here is that rolls of 8mm edge insulation should be used. They should be used on all external and internal walls.

This is to allow the screed to expand freely and also it doesn't allow moisture from the screed been poured to soak into the plasterboard walls.

Rossdarragh1

Thanks for that. Will the plastic cover not do the same job ,by not allowing moisture within the screed to soak into the plasterboard. It was my understanding that this was the reason for turning the plastic up the walls once it's laid over the floor insulation. I thought the edging just gave a better seal and prevented thermal bridging which isn't an issue for me with an insulated slab.

delfagio wrote: »

What should be done here is that rolls of 8mm edge insulation should be used. They should be used on all external and internal walls.

This is to allow the screed to expand freely and also it doesn't allow moisture from the screed been poured to soak into the plasterboard walls.

delfagio

Rossdarragh1 wrote:

Thanks for that. Will the plastic cover not do the same job ,by not allowing moisture within the screed to soak into the plasterboard. It was my understanding that this was the reason for turning the plastic up the walls once it's laid over the floor insulation. I thought the edging just gave a better seal and prevented thermal bridging which isn't an issue for me with an insulated slab.

Yes lapping the plastic up the walls will stop moisture soaking into plasterboard but you need to put in the 8mm edge insulation rolls around all walls and fixed obstacles.

Just to be clear, I'm not referring to perimeter insulation just the edge insulation. I was in the same position you are, I had insulated plasterboards on all external walls which ran to approx 100mm above my subfloor, so this acted as my perimeter insulation. I then installed the edge rolls after I laid the floor insulation.

The reason for the edge insulation is not really from a thermal point of view but is only to allow room for the screed to expand freely without cracking.

JimmyMW

delfagio wrote: »

Yes lapping the plastic up the walls will stop moisture soaking into plasterboard but you need to put in the 8mm edge insulation rolls around all walls and fixed obstacles.

Just to be clear, I'm not referring to perimeter insulation just the edge insulation. I was in the same position you are, I had insulated plasterboards on all external walls which ran to approx 100mm above my subfloor, so this acted as my perimeter insulation. I then installed the edge rolls after I laid the floor insulation.

The reason for the edge insulation is not really from a thermal point of view but is only to allow room for the screed to expand freely without cracking.

Interested in what you are saying re screed expansion, however I am not entirely sure of the detail you are describing, could you show us a drawings or sketch?

BryanF

Wtf

I'm out

JimmyMW

delfagio wrote: »

Yes lapping the plastic up the walls will stop moisture soaking into plasterboard but you need to put in the 8mm edge insulation rolls around all walls and fixed obstacles.

Just to be clear, I'm not referring to perimeter insulation just the edge insulation. I was in the same position you are, I had insulated plasterboards on all external walls which ran to approx 100mm above my subfloor, so this acted as my perimeter insulation. I then installed the edge rolls after I laid the floor insulation.

The reason for the edge insulation is not really from a thermal point of view but is only to allow room for the screed to expand freely without cracking.

BryanF wrote: »

Wtf

I'm out

Sorry I have just re read the thread and I see what your saying now, you are separating edge insulation into perimeter insulation (external walls) and edge insulation (internal walls). I taught you were on about something completely new and I was intrigued, sorry my fault.

Fair point Bryan

Rossdarragh1

delfagio wrote: »

Yes lapping the plastic up the walls will stop moisture soaking into plasterboard but you need to put in the 8mm edge insulation rolls around all walls and fixed obstacles.

Just to be clear, I'm not referring to perimeter insulation just the edge insulation. I was in the same position you are, I had insulated plasterboards on all external walls which ran to approx 100mm above my subfloor, so this acted as my perimeter insulation. I then installed the edge rolls after I laid the floor insulation.

The reason for the edge insulation is not really from a thermal point of view but is only to allow room for the screed to expand freely without cracking.

I'd be looking something like this so:

https://youtu.be/DteppEZi-xw

Rossdarragh1

Rossdarragh1 wrote: »

I'd be looking something like this so:

https://youtu.be/DteppEZi-xw

Without the upstand of course