Floor Insulation Queries

Biff02008

Hi Guys,

Am currently in the middle of a self build and am coming near the stage where I need to start laying the floor insulation for UFH. So far I haven't done much of the build myself, but am thinking that to try and save a few bob I might tackle the laying of the floor insulation myslef over the christmas while I have a few days off.

Quick detail: House is 2700 sq ft, ground floor has a 4 inch subfloor poured from the start, now going to lay 150mm Kinsgpan TF70 floor insulation,( 2 layers, first 100mm and second 50mm) then UFH pipes and then 75mm sand/cement screed.

First floor will be one layer of 50mm Kingspan TF70 floor insulatio layed on the precast slabs, UFH pipes and then 50mm sand/cement screed.

As I haven't laid floor insulation before I have a few questions that I hope the more knowledgable people here could help me with.

1. Does the first layer of insulation (100mm sheet on ground floor and 50mm sheet on first floor) need to be fixed to the subfloor with screw fixings or is it enough just to get the sheets to fit tightly.

2. Do I need to tape all the joints between each of the sheets?

3. For the perimiter insulation, I was going to use 50mm on the external walls and 25mm for the internals. Does the perimeter insulation only need to be the depth of the screed (75mm ground floor, 50mm first floor) or should the perimter insulation be the full 225mm from subfloor to finished floor level and then floor insulation butted tightly up to it?

4. I presume that all joints in the perimiter insulation need to be taped. Do I also need to fix this insulation to the perimiter walls in some way.

Thanks in advance for any help given.

Biffo

peterc14

I asked a similar uestion recently but unfortunatley not too many replies... has anyone on here laid ufh insulation before?

decnev

No expert but from what i know:
1: Insulation does not need to be fixed to sub-floor. Tightly butted together but no bowing.
2:Taping not required. With your two layers of insulation stager the joints i.e. lay the second layer at 90 degrees to the first layer.
3: Its easier to hold the perimeter insulation in place if it's held behind the floor insulation. Place the perimeter insulation behing the top layer i.e. 75mm + 50mm = 125mm for ground floor.
4: If perimeter insulation is butted tightly together, taping is not required. You will be running a sheet of 500gage plastic over all your floor insulation, which you will tape to the walls just over you perimer insulation / floor height [excess to be cut away after screed has set].

Hope this helps?

stevo30

Just my opinion but this is a hugely important part of your house to get right insulation wise, i would use someone who has worked in this line of work before. if you make a mistake and discover cold bridging a year down the line it won't be easy to rectify. just my two cents not worth cutting corners with insulation on a new build

BryanF

Re perimeter insulation: research foamglass - to stop any cold bridge issues

kboc

Biff02008 wrote: »

Hi Guys,

Am currently in the middle of a self build and am coming near the stage where I need to start laying the floor insulation for UFH. So far I haven't done much of the build myself, but am thinking that to try and save a few bob I might tackle the laying of the floor insulation myslef over the christmas while I have a few days off.

Quick detail: House is 2700 sq ft, ground floor has a 4 inch subfloor poured from the start, now going to lay 150mm Kinsgpan TF70 floor insulation,( 2 layers, first 100mm and second 50mm) then UFH pipes and then 75mm sand/cement screed.

First floor will be one layer of 50mm Kingspan TF70 floor insulatio layed on the precast slabs, UFH pipes and then 50mm sand/cement screed.

As I haven't laid floor insulation before I have a few questions that I hope the more knowledgable people here could help me with.

1. Does the first layer of insulation (100mm sheet on ground floor and 50mm sheet on first floor) need to be fixed to the subfloor with screw fixings or is it enough just to get the sheets to fit tightly.

2. Do I need to tape all the joints between each of the sheets?

3. For the perimiter insulation, I was going to use 50mm on the external walls and 25mm for the internals. Does the perimeter insulation only need to be the depth of the screed (75mm ground floor, 50mm first floor) or should the perimter insulation be the full 225mm from subfloor to finished floor level and then floor insulation butted tightly up to it?

4. I presume that all joints in the perimiter insulation need to be taped. Do I also need to fix this insulation to the perimiter walls in some way.

Thanks in advance for any help given.

Biffo

I have just done this. It took me ages but I am really please with the job. Plumber said he never seen such a particular job.

1. I lay 50mm layer down first straight on sub floor, no fittings (This would create cold bridging possibly). Make all boards tight fit. Any gaps between sheets fill with expansion foam. Place a concrete block on the areas were expansion foam is done. The expanding action of the foam lifts the boards up. A bit of weight is needed here. When it sets after an hour or so then lift off.

2. Then a layer with 100mm. Again tight together and fill gaps with expansion foam insulation and concrete blocks.

3. Use grip fill or a similar product to stick the perimeter insulation to the edge. It does not take that much to stick to wall. TAPE ALL JOINTS and HOLES OR DENTS IN FLOOR BOARDS AT THIS POINT WITH FOIL TAPE. This ensures less heat loss and you don't need to put down any gauged plastic as the foil is water proof. Throw off the boots/shoes and walk in stocks to save the boards being damaged further.

4. I taped all joints where bottom of perimeter strip meets insulation floor boards with airtight tape. Especially around the doors (and any windows/patios which sit at ground level) area.

The last point may seem pointless. But when i was doing this, the draft that blew up this area was unbelievable.

I done this my self rather than pay for somebody else. It takes time and patiences and I know it was done right as I done it. So if the house is cold (which it is not so far!) then i know the floor insulation is not to blame

Hope this helps

Good luck

Dupont

when i lay it i just try to get good tight joints never tape them and there is no need to screw it.anybody could put it down just use full sheets wherever possible and cut pieces to fit. some people use a strip of 25mm insulation around the edge to allow for expansion. you know u have to put down a dpm under the insulation(top of subfloor) u probaly have radon barrier under subfloor but still use it. 1200 gauge polethene will do and dont for get to stagger joints

peterc14

kboc wrote: »

TAPE ALL JOINTS and HOLES OR DENTS IN FLOOR BOARDS AT THIS POINT WITH FOIL TAPE.

I taped all joints where bottom of perimeter strip meets insulation floor boards with airtight tape.

Just wondering what type of foil tape & airtight tape you would recommend and where you bought (pm if not allowed to state).

Also would it be too extrem to tape the joints and then also lay a membrane?

t wex

Biff02008 wrote: »

First floor will be one layer of 50mm Kingspan TF70 floor insulatio layed on the precast slabs, UFH pipes and then 50mm sand/cement screed.

75mm sand cement wil work fine downsairs but the 50mm sand cement you propose upstairs is too shallow for a sand cement mix. It will shrink and cup and crack.

50mm is fine for a liquid floor screed and will give the recommended 30mm cover over the pipes.

peterc14 wrote: »

Just wondering what type of foil tape & airtight tape you would recommend and where you bought (pm if not allowed to state).

Also would it be too extrem to tape the joints and then also lay a membrane?

Taping joints-
Generally insulation is only taped to stop screed going down between it so use the cheapest tape that will stick. the 2" tape they use to close boxes or the tape branded with the local building supplies branding. if using a dry sand cement mix tightly butting insulation together should suffice. For a wet mix or almost perfect insulation put down a roll of polythene.

Airtight tapes to join Insulation-
Often the slab itself is used as the airtight layer, or better still the radon barrier (if part of it is still visible at the foot of the wall). I wouldn't use a airtight tape here as they are over €1.20/m. to connect floor or radon barrier to walls it would be worth using one that can be plastered into walls.

Floor insulation as an airtight layer-
I don't need to poke holes in that idea because your underfloor heating installer will when fixing down the pipes:D

Foil Tapes in floors-
There is no need for foil tape. You won't be taking from the quoted performance of the foil covered insulation. The foil is only beneficial in other applications where there is a minimum 25mm air cavity which can happen in walls & roofs but obviously not floors.

kboc

peterc14 wrote: »

Just wondering what type of foil tape & airtight tape you would recommend and where you bought (pm if not allowed to state).

Also would it be too extrem to tape the joints and then also lay a membrane?

ah yes, welcome to the "nanny" category within boards.ie. I shall PM you the name for airtight tape. The foil tape is any standard tape got from a decent builders suppliers.

Just a change in detail to what i wrote. The air tight tape was put on before the perimeter strip. I taped the floor insulation boards to the wall.

Maybe this is overkill in some peoples eyes, but i have services ducts coming in thro the sub floor for plumbing, electrics etc (stops the ramp course/radon barrier being punctured) and these produce draughts. I also have windows siting on concrete lintels at the finished floor level. All areas for huge amounts of air to seep in.

It is not everybody's cup of tea, but it is your own house and you'll only do it once, then do it with NO regrets. Don't be doing "i wish....", i know so many of my family who done this and hugely regret not paying a bit more attention to it.

Good Luck

Biff02008

hi guys, sorry for not getting back sooner...been quite busy at work and not the house unfortunately!!

Anyway, thanks for all the replies, it is very much appreciated and all advice will be taken on board.

t_wex, thanks for pointing that out. My original post was incorrect. Ground floor will be 75mm sand/cement screed and 1st floor will be 50mm hemi hydrate liquid screed.

Kboc, I notice you yayed the 50mm sheet before the 100mm sheet on the gound floor. Did you have any problems with this? Just curious as I thought you would lay the opposite way but I'm guessing that laying the 100mm sheet second is better protection when people are walking on it!

Floor insulation was all delivered today so hoping to get cracking over the weekend at it. I have one more question if thats OK? I have insulated drylining boards on the external walls of my house. However, when the plasterer installed the slabs, they are currently 4 to 5 inches down from finsihed floor level. Hope that makes sense....but basically my subfloor is 9 inches below what will be finsihed floor level, being made up of 6 inches insulation and 3 inch screed. So on the external walls there is a gap of 3 to 4 inches from subfloor to bottom of the insulated board.

My question is do I need to cut away these excess inches from the insulated drylining boards in order to leave the 9 inch gap from bottom of insulated board to subfloor before laying my floor insulation. Or can insulated boards act as the perimiter insulation? I'm guessing that they cant as moisture from the screed might seep up through the insulated slab over time?

Should the top of the floor screed finish just under the bottom of insulated drylining slabs?

Also, is there an upper limit on the depth on perimiter insulation on external walls? ie. is 50mm the most that you should go or can you go 75mm?


I would appreciate the thoughts of anyone with the knowledge?

kboc

Biff02008 wrote: »

hi guys, sorry for not getting back sooner...been quite busy at work and not the house unfortunately!!

Anyway, thanks for all the replies, it is very much appreciated and all advice will be taken on board.

t_wex, thanks for pointing that out. My original post was incorrect. Ground floor will be 75mm sand/cement screed and 1st floor will be 50mm hemi hydrate liquid screed.

Kboc, I notice you yayed the 50mm sheet before the 100mm sheet on the gound floor. Did you have any problems with this? Just curious as I thought you would lay the opposite way but I'm guessing that laying the 100mm sheet second is better protection when people are walking on it!

Floor insulation was all delivered today so hoping to get cracking over the weekend at it. I have one more question if thats OK? I have insulated drylining boards on the external walls of my house. However, when the plasterer installed the slabs, they are currently 4 to 5 inches down from finsihed floor level. Hope that makes sense....but basically my subfloor is 9 inches below what will be finsihed floor level, being made up of 6 inches insulation and 3 inch screed. So on the external walls there is a gap of 3 to 4 inches from subfloor to bottom of the insulated board.

My question is do I need to cut away these excess inches from the insulated drylining boards in order to leave the 9 inch gap from bottom of insulated board to subfloor before laying my floor insulation. Or can insulated boards act as the perimiter insulation? I'm guessing that they cant as moisture from the screed might seep up through the insulated slab over time?

Should the top of the floor screed finish just under the bottom of insulated drylining slabs?

Also, is there an upper limit on the depth on perimiter insulation on external walls? ie. is 50mm the most that you should go or can you go 75mm?


I would appreciate the thoughts of anyone with the knowledge?

Correct, but don't let too many walk on it. When I was working on it I took shoes off. Never a chance getting plumbers to do this when they are in and out of house installing it!!!!

good luck

muffler

Dont forget to include a polythene sheet between the screed and insulation.

creedp

I will shortly be going down this road and am interested in the airtightness aspect of the job. Is it better to try to apply airtighness tape to the bottom of the external walls and subfloor or would it be sufficient to tape the polythene on top of insulation to the external walls. In the latter case the fact that the polythene is taped along the perimeter and the weight of slab on polythene result in a airtight seal?

I was considering taping the wall to floor before putting in insulation but given the nature of the surfaces, i.e. concrete dust, rippled surface of subfloor, etc would taping the polythene to the wall be more effective?

Would another option be be to run a sheet of polythene along perimeter wall, tape it to wall but not to the subfloor as the weight of insulation and screed would create an airtight seal against the subfloor?

It is the same story upstairs as I have slabs but although I insisted and he reluclantly agreed to wrap the slabs in a membrane when I got to the site the slabs were on and he hadn't used the membrane - again what would be the best option among those above for this situation?

All views on the above are very much welcomed as I am constantly fighting a losing battle with builder on airtightness with him considering everything being over the top. Only yesterday evening I called to site to find he had started to slab the attic space (its a roomy attic but will not be used for living accommodation just storage and possibly occasional games room). He put polythene underneath the insulated slabs as an airtightness measure (as I have MHRV and the rest of the house has been made airtight) but didnt attach to gables; didn't tape overlaps; where there are partitions didn't bring to polythene out under the slabs so it could be sealed to partition wall; didn't seal polythene around velux windows surrounds but instead manage to rip it to shreds it looked like it was torn rather than cut; at the corners the polythene is just bunched and stapled into a big heap; etc. Needless to say I nearly collapsed!

So all advice welcomed!

Thanks

Biff02008

Thanks again for the advice kboc and muffler!

Any ideas on the insulated drylining boards, do I need to cut them away to the right level? I think I do, but just want to get confirmation before I spend all that time doing it.

Cheers

peterc14

For insulation being put down on the first floor...

The hollowcore slabs are not 100% level (only slightly off in some place i.e where they abut each other)... therefore should I use something (sand?) to get the floor exactly level prior to the insulation and screed?

Dupont

i would put down insulation as normal and the screed would take out any discrepencies

sydthebeat

peterc14 wrote: »

For insulation being put down on the first floor...

The hollowcore slabs are not 100% level (only slightly off in some place i.e where they abut each other)... therefore should I use something (sand?) to get the floor exactly level prior to the insulation and screed?

they never are.... as dupont says, the screeding will resolve this

soldsold

What I did:

Use more than one layer of insulation and stagger the joints. This takes out any need to tape the joints.
Use cheap insulation (EPS) in thicker sheets.
Put the edge insulation in before the last insulation level goes in, ie have 100mm of it covered by the flat insulation sheets so it stays in place.
I used 3 layers of insulation with 1200 gauge polyethylene membrane on the first layer. Its fitted tightly so even if concrete got through a couple of gaps in the first layer, it cant get through the second.

Im all for getting the details right but I do think some of the advice on this thread, while being perfect, are a bit of an overkill.

tred

soldsold wrote: »

What I did:

Use more than one layer of insulation and stagger the joints. This takes out any need to tape the joints.
Use cheap insulation (EPS) in thicker sheets.
Put the edge insulation in before the last insulation level goes in, ie have 100mm of it covered by the flat insulation sheets so it stays in place.
I used 3 layers of insulation with 1200 gauge polyethylene membrane on the first layer. Its fitted tightly so even if concrete got through a couple of gaps in the first layer, it cant get through the second.

Im all for getting the details right but I do think some of the advice on this thread, while being perfect, are a bit of an overkill.

Just wondering regarding the perimter strip. Should it be matching the height of theinsulation, or the height up to the screed?. So for say 100mill tf70, should the permiter strip be 100 in height or 100 + floorscreed.

soldsold

Not sure if Im following you tred, the insulation perimeter strip is around the concrete screed for its full height.

So its insulation layer, with concrete 75mm on top of insulation, and wrapping the insulation is a perimeter of insulation 75mm high and as wide as you like - usually 50mm but I used 100mm with the top tapered to 25mm or so.

If you picture a rectangular flower window box full of clay, the box is the insulation, the clay is the concrete screed.

tred

soldsold wrote: »

Not sure if Im following you tred, the insulation perimeter strip is around the concrete screed for its full height.

So its insulation layer, with concrete 75mm on top of insulation, and wrapping the insulation is a perimeter of insulation 75mm high and as wide as you like - usually 50mm but I used 100mm with the top tapered to 25mm or so.

If you picture a rectangular flower window box full of clay, the box is the insulation, the clay is the concrete screed.

Ah I get ya. So its probably visible on the finished floor, the perimeter strip.