underfloor heating upstairs- should i insulate above precast slab

Karro44

I'm looking at building a new house and could do with some advice.

I'm building a 2 storey house with underfloor heating on both floors. I'm also putting in a concrete floor for upstairs. According to my engineer this will be 200mm hollowcore precast slabs.

Does anyone know if i need to put insulation above the precast slab before laying the underfloor heating.

Thanks
D

Outkast_IRE

Karro44 wrote: »

I'm looking at building a new house and could do with some advice.

I'm building a 2 storey house with underfloor heating on both floors. I'm also putting in a concrete floor for upstairs. According to my engineer this will be 200mm hollowcore precast slabs.

Does anyone know if i need to put insulation above the precast slab before laying the underfloor heating.

Thanks
D

This has been asked many times before and the answer after discussion is usually yes.

You want to be able to direct the heat to an extent and there will be a massive warm up time for the upstairs underfloor otherwise as it will need to heat the entire hollowcore slab plus the screed or similar you pour above it.

Using the insulation layer you are only heating the screed layer above the underfloor pipes. This leads to a much more responsive system with lower heat up time.

Karro44

Hi OutKast_IRE,

Thanks for responding. I'm going to put 75mm insulation above the precast floor. I agree its better to have a more responsive heating system and also to prevent any heat loss between the concrete slab and the cavity walls.

I'm using Qiunnlite blocks on the inner leaf of the cavity. Do you know of any issues/problems in using these blocks with underfloor heating?

Thanks,
D

Outkast_IRE

Karro44 wrote: »

Hi OutKast_IRE,

Thanks for responding. I'm going to put 75mm insulation above the precast floor. I agree its better to have a more responsive heating system and also to prevent any heat loss between the concrete slab and the cavity walls.

I'm using Qiunnlite blocks on the inner leaf of the cavity. Do you know of any issues/problems in using these blocks with underfloor heating?

Thanks,
D

No there should be no problem with Quinnlite blocks and underfloor heating, underfloor heating is a relatively low temperature, so should not have any effect.

Calahonda52

OP,
is engineer happy to use Quinnlite on inner leaf to receive the hollow core?
I don't need to know but you need to check:)
You need perimeter insulation as well.

Just make sure every knows how the height adds up up stairs as I have seen plenty examples where builders assume its X mm up stairs and then discover it should have been X plus 50 or what ever and it ends up being cut back as top of clockwork is too low

Are u using same insulation down stairs?

Karro44

Hi Calahonda52,

Thanks for the advice. My engineer has specified 215mm 7N/mm2 block work for any load bearing walls. He understands that these will be quinnlite blocks and doesn't have any issues with it. Any reason he would not want to use quinnlite blocks?

I had my architect increase the room heights to accommodate a concrete first floor when submitting for planning. I'll keep an eye on this during construction. Thanks.

I'm using 150mm insulation for the ground floor insulation, this should give me a U-value of 0.11. Based on a floor area of 108m2 and a perimeter of 58m.

Do I need perimeter insulation if I am using quinnlite blocks?

Calahonda52

Oaky so the inner leaf is 215 mm wide?
Whats the rest of the wall make up.
Yes I would add perimeter insulation up stairs

Are you going for MHVR?
If so whats the airtightness layer on the quinn lite?

I ask because if it is sand/cement plaster, there are some plasterers who don't like plastering quinn lite because its so smooth and softish
http://www.boards.ie/vbulletin/showthread.php?p=82898605


Down stairs, whats the plan: 3 layers at 50 a time with staggered joints.
If so then what upstairs for the 75?
The reason I ask is that this is a typical scenario where it can go pear shaped: builder orders all 50 mm and 50 end up up stairs, or 100 mm:)

Karro44

Hi

Wall make up is 100mm external wall with 150mm cavity consisting of 110mm insulation and 40mm cavity. Inner leafs upstairs are 100mm and down stairs consists of 100mm and 215mm on load bearing walls. All inner leaf walls are quinn lite.

I understand the limitation with plastering theses walls but Im only at the tendering stage so I'll wait and see what contractor says.

I'm not planning on putting in MHRV at least not at the moment. If budget allows I'll put in the pipework for the ground floor and revisit at later date.

Downstairs the plan is 100mm and to 50mm staggered as you said. For upstairs i was just putting in 75mm on its own.

Calahonda52

Thanks.
I would do the MHRV, even at the price of reducing the overall size of house, especially with that floor , retro upstairs wont really be an option.
In addition 1.2.2.1 of Part F will kill you as you drive up the airtightness levels