First floor UFH on Beam and Block - Insulation issue.

[MMcGill]

Hi - we're using beam and block on all three floors of our new build and are looking to install UFH on all three levels. Ground floor no issue - K103 being installed and allowed for, but it now comes to light that the architect didn't specify insulation on the floor build up for first and second floors (yes I'm annoyed and should have spotted this - but too late now).

 

So I'm looking for your advice, as I see it I have three options;

 

1 - Lose headroom on these floors to allow for insulation - I'd clearly rather not lose headroom

 

2 - Insulate the void under the beam and block on first and second floor - this void will be used for MVHR ducts, wiring and downlighter where required, thought is that we could fill around the ducts leaving enough room for everything else.

 

3 - Move to radiators on first and second floor.

 

No ideal option as I see it but probably attracted most to option 2 as the best compromise - what would you do? Any thoughts appreciated.

 

For reference insulation is as follows;

• Floor - Kingspan 110mm K103 = 0.11U 
• Walls - Kingspan K106 115mm with 10mm void (current spec would then give a void of 20mm) = 0.14U 
• Roof -  150mm K107 to full fill and 57.5mm K118 used under = 0.11U 
• Windows - All triple glazed so assuming 0.8U

[MikeGrahamT21]

Assuming you are going full on with airtightness, I can’t see why you would need insulation on first and second floors for any type of heating system? Having it would stop some of the heat rising from other floors?

 

I’m sure someone will correct me if I’m wrong here…

[Adam2]

14 minutes ago, MikeGrahamT21 said:

Assuming you are going full on with airtightness, I can’t see why you would need insulation on first and second floors for any type of heating system? Having it would stop some of the heat rising from other floors?

 

I’m sure someone will correct me if I’m wrong here…

I too wondered that and suggested not including it but the rationale I believe was to allow faster heating response times in the floor above the UFH by not loosing heat into the concrete floor below the screed containing the UFH pipes - we have 150mm concrete planks. If you have an incredibly low rate of temp change which is more or less uniform across the building then maybe the heat transfer to the B&B would not matter very much so you could save money and headroom 🙂 In the end we put in 25mm and we will never know if this helps or not 🙂 

 

@MMcGill I don't see any real benefit in option 2 - by the time the insulation works it'll be after the heat has passed down through the beam + block floor. It would of course stop some heat transfer to upper floors but that's not I believe the intention of insulating under the UFH. Not sure what thickness insulation you were planning on using on the upper floors?

 

 

[Conor]

What thickness screed have you allowed for? If its 100mm, you can easily get away with 50mm insualtion then 50mm liquid screed.

 

I wouldn't even consider your other two options, you can just for the UFH directly to the floor I'd there's no room for insualtion.

[MMcGill]

I’m only at 50 to 60mm screed already, from what I’ve read the be edits of the insulation is to prevent the first floor UFH unintentionally heating the ground floor as well along it harder to control on that floor - think you’re saying don’t worry about it though?

[Thorfun]

Could you potentially use those insulated blocks others have mentioned on here in other threads instead of normal concrete blocks? Probably expensive but might be a solution worth investigating?

[MikeGrahamT21]

10 hours ago, MMcGill said:

I’m only at 50 to 60mm screed already, from what I’ve read the be edits of the insulation is to prevent the first floor UFH unintentionally heating the ground floor as well along it harder to control on that floor - think you’re saying don’t worry about it though?

 

I think the heating effect to the floor below would be marginal, if at all, especially since you have a void for services too.

 

Can I ask also, what is the reason for block and beam on all floors, is it purely for underfloor heating? I've not seen this used on another build before other than ground floor. Depending how far along you are, how about swapping out for i-beam/web joists, chipboard/osb floor on top, insulation with underfloor heating pipes in it (the routed boards), and screed on top? You can play about with depths then also, as the void could be included within the joists.

[Dave Jones]

you dont need insulation on the intermediate floors. 

 

Get the shell airtight instead and you be laughing.

[MMcGill]

The block and beam is defo a bit overkill but really wanted to isolate each floor and absolutely hate squeaky floors so will never have to deal with that! This is my forever home so wanted to get the fabric as high quality as possible.

Air tight aiming for 1 or less and the insulation is pretty good throughout so hopefully we’ll end up with a very efficient home.

 

thanks for the comments - my concerns have dropped somewhat!

[BotusBuild]

Take a look at this for starters - option 2 or 3 would be suitable - Nuheat is not your only choice for getting the products

 

 

 

 

[Nickfromwales]

3 hours ago, Dave Jones said:

you dont need insulation on the intermediate floors. 

 

Get the shell airtight instead and you be laughing.

+1. "Airtightness, airtightness, airtightness".

Ventilation heat loss is the killer, fabric heat loss comes second. If you manage airtightness then the heating issue becomes easily manageable ( in a true low-energy dwelling ). I took 3 days for my current clients PH to drop 2.7^oC after I set the ASHP to 15^oC flow temp!! Clients stated that the property was a bit too warm to work in ( sweeping / tidying up etc ) at circa 19.0^oC on the central room stat! That's without the MVHR fired up yet, and the doors opening and closing all day long with trades in / out.

 

 

Did I mention airtightness?

[Nickfromwales]

+1 to no upper floor(s) insulation ( other than acoustic if necessary / mandated by BCO ). 

[Nickfromwales]

1 hour ago, MMcGill said:

The block and beam is defo a bit overkill but really wanted to isolate each floor and absolutely hate squeaky floors so will never have to deal with that! This is my forever home so wanted to get the fabric as high quality as possible.

Air tight aiming for 1 or less and the insulation is pretty good throughout so hopefully we’ll end up with a very efficient home.

 

thanks for the comments - my concerns have dropped somewhat!

This can all be achieved with a posi-joist deck tbh.

I have installed many, been around loads, have installed UFH atop, tiled atop and for all uses of spaces ( bedroom / other ) with ZERO squeaks and ZERO issues with deflection. You will get deflection, but not anything where you will stop and make a note of it ( if you install the posi's properly and reinforce with stiffer joists and never more than 400mm o/c's.

I do nothing other than help create forever homes for private self-build clients, so failure is defo not an option, quite the opposite. B&B is massive overkill AFAIK.

[Dave Jones]

another vote for pozi's. correctly glued deck doesnt squeek and they bounce less than beams.

[MMcGill]

Thanks - block and beam on first floor is already on, agree it was probably overkill but not a detriment so happy enough…

[MMcGill]

First floor UFH with no insulation under it - not seen any issues then? Had heard that it could cause issues in the ground floor effectively heating from below and above at once… 

[Dave Jones]

heat rises etc.

[MikeGrahamT21]

3 hours ago, MMcGill said:

First floor UFH with no insulation under it - not seen any issues then? Had heard that it could cause issues in the ground floor effectively heating from below and above at once… 

 

Heat won't go down into the room below, the only issue you may find is that the UFH's responsiveness is slow on this floor, since some of it will soak into the slab, however that slow responsiveness will end with a smoother heat curve, rather than fluctuations. If this is an issue, then any amount of insulation will slow this soak.

[ADLIan]

Under the 2021 version of Approved Doc L intermediate floors with heated floor systems require thermal insulation (as well as acoustic requirement).

[MikeGrahamT21]

4 hours ago, ADLIan said:

Under the 2021 version of Approved Doc L intermediate floors with heated floor systems require thermal insulation (as well as acoustic requirement).

Just checked this and yeah you’re right, a very bizarre specification but here it is

 

 

and the corresponding thickness of XPS showing R value

 

 

so assuming this is wet underfloor heating, it’ll need around 25mm XPS, which should be doable with 20mm PIR.

 

can’t quite get over that requirement, as it’s all inside the thermal envelope 🤷‍♂️

[Dave Jones]

yes this is a little barmy but 30mm of EPS will help with sound transmission I guess, just need to allow for the FFL on intermediate floors now as well...

 

or

 

put the pipes in without insulation and just dont connect them at manifold. sign off then re-connect.

 

 

Edited March 30, 2023 by Dave Jones

[Temp]

We have a beam and block first floor with UFH.  In some rooms we went for 200mm wide 21mm thick Engineered Oak flooring with no screed.

 

The UFH system we choose for this uses a foiled insulation with grooves for pipes. This was laid on a layer of PIR. Both the UFH and PIR was laid between "battens" that are the same depth to support the Engineered Oak floor. 

 

It works but our flow temperatures are probably higher than you are aiming for.

 

 

Edited March 30, 2023 by Temp

[Dave Jones]

the goal should be build the house right so the only heating required is the ground floor slab. if the heat losses mean you need more than the thermal envelope isnt good enough.

 

Can see why the regs are written to cover the legoland builds which make up the majority of new build and are crap as we all know.

[iMCaan]

@MMcGill Thanks for creating this post and others for sharing your comments/suggestions. I too have the same issue.

What thickness should the insulation be on the beam and block first floor? After reading the comments in the post, I'm now considering 25mm thick PIR insulation board instead of 50mm with liquid screed.

 

@MMcGill Did you go with UFH on the first floor? What thickness insulation did use? Was it above the beam blocks or in the voids below? Would love to hear about your UFH setup on the first floor?

 

Much appreciated. Thanks