Insulation on hollowcore for UFH

Holla23

Hi,

Just wondering what are the recommended levels of insulation & screed when using UFH upstairs on hollowcore.

At the moment planning to go with 30mm insulation and 60mm of concrete screed. We are also going to use a HP to heat the UFH so not planning to go with the flow screed.

Thanks.

therightangle

Holla23 wrote: »

Hi,
We are also going to use a HP to heat the UFH so not planning to go with the flow screed.

Hi, whats the connection/logic in the above? Cheers

Holla23

I'm no expert but am staying away from the flow screed as while it heats up quicker it also cools quicker which causes the HP to runs it cycle more frequently.

BryanF

Holla23 wrote: »

I'm no expert but am staying away from the flow screed as while it heats up quicker it also cools quicker which causes the HP to runs it cycle more frequently.

only a problem if your building fabric and heat recovery is poor

Holla23

Thanks Bryan.

Just wondering if you would you recommend insulation on the hollowcore? Going with HRV and at the moment have 150mm pumped cavity.

Also debating whether to go with internal insulaion on the external walls or not. Internal walls are block and a large portion of the living area are tiled so that will take care of the thermal mass. I'm concerned that drylining would make it more difficult to achieve airtightness than the plaster finish. What are your thoughts on that?

BryanF

Holla23 wrote: »

Thanks Bryan.

Just wondering if you would you recommend insulation on the hollowcore? Going with HRV and at the moment have 150mm pumped cavity.

Also debating whether to go with internal insulaion on the external walls or not. Internal walls are block and a large portion of the living area are tiled so that will take care of the thermal mass. I'm concerned that drylining would make it more difficult to achieve airtightness than the plaster finish. What are your thoughts on that?

no not the first slab, dont bother

plaster the inside, widen the cavity

Musicman2006

Holla23 wrote: »

Hi,

Just wondering what are the recommended levels of insulation & screed when using UFH upstairs on hollowcore.

At the moment planning to go with 30mm insulation and 60mm of concrete screed. We are also going to use a HP to heat the UFH so not planning to go with the flow screed.

Thanks.

Presumably you'll also have a 75mm structural screed on top of your hollowcore units? Without it you will have no peripheral ties or slab diaphragm action and of course wont meet the regs or the requirements of the masonry design code of practice. I'm a structural engineer but I'm just raising it now because so many people leave this out of their self builds because 'it'll be grand!'..

Holla23

Thanks guys.

At the moment 75mm is allowed for the structural screed but there was no allowance for insulation so just needed to confirm the allocated size for insulation/screed for the floor on the hollowcore.

@ BryanF,

The cavity is already built so too late to widen it now! :mad:

Would you still recommend going withoutdrylining the external walls.

Thanks!

BryanF

Holla23 wrote: »

@ BryanF,

The cavity is already built so too late to widen it now! :mad:

Would you still recommend going withoutdrylining the external walls.

Thanks!

well i suppose you should take a holistic view,

• whats your thermal bridges and detailing like
• what overall u-value windows,
• level of proposed air-tightness

I cant answer this without knowing your build. we could debate this all day. extra wall insulation V thermal mass: money spent on dry-lining V getting air-tightness right: EROEI of insulation V 'actual' renewable heat source.:eek: me heads wrecked just thinking about it:D

is your architect any good? has anyone suggested a BER? or better a PHPP calculation?

Holla23

Thanks Bryan.

We have sorted a BER and PHPP calculation so we are striving to get a value to which the budget will allow - A3 or B1. It would be nice to go all out for the A1 but unfortunately we don't have the funds to stretch that far.

My architect is very good and has gone through the various pros and cons of the building methodoliges available but it gets a little confusing when there is so much conflicting information! The Boards is where I try to get my head around things but sometimes it confuese me even more!!!

Cheers.