Edward

Insulating between joists to accept UFH

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Hi everyone. New to the forum as i'm looking for some advice please.

 

I am looking to insulate between the joists of my suspended timber floor (ground level) to an acceptable standard in order for my plumber to install UFH. We will be most likely using the REHAU spreader plate system so not to raise the FFL. Ive a few questions about the process:

 

1) Do i need to be concerned about moisture/condensation - should i install a DPC type membrane and if so, should this go above or below the insulation?

2) Does it matter if the spreader plates are touching the insulation, or do i not need to be too concerned about the space between the top if the insulation and the bottom of the plates?

3) Should i ensure any gaps between the insulation and the joists, external walls of the house are as air tight as possible? Should i use a tape or expanding foam?

4) Finally, im torn between using a rockwool type insulation or a kingspan board which will need cutting to size. Any opinions of which to use and why is appreciated.

 

Our builder has quoted £5k for this aspect of the renovation (i asked him to achieve a u value of 0.25w/m2 or less), and as far as im aware its relatively straight forward.

 

Any advice is greatly appreciated, thanks in advance

 

Edward

 

 

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No ones answering so I will get the ball rolling. 

I think your ideas are flawed in nearly every aspect, the u value your looking at is pretty poor, I think your heat losses down will be large and you will spend half of your heating bill heating the gap under the floor. 

 

Are those plates designed for ground floor ? I thought they where used more fore first floor. 

 

If they are designed for ground floor then there must be a design spec for them. 

 

The problems you will have is stopping heat escaping downwards, (obviously) but also the airflow and drafts under the floor will be large so sucking the heat from the floor above. 

 

The majority of builders wont have any idea on the details required to make this work. 

 

What sort of depth are the joists?

 

 

 

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got any plans with detail

 how much space under this floor ?

Is floor actually in yet ?

If not drop joist hangers down and do it all above .

 might be simpler and cheaper in long  run?

If not possible

you could achieve both dpc and insulation by getting CLOSED cell foam sprayed under floor there after plumber+ other trades  have finished

quotes I,ve had for this type of insulation vary around £30-40 per sq m 

would be done in one day by a contractor 

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Ok thanks for the reply.

 

I dont have any plans yet. Yes the floor is in, the house was built in the 30s. Its my kitchen floor, and the depth of the space underneath the floor is enough to stand up in. The u value of 0.25, as far as im aware, is the U value which new builds are required to achieve. What u value should i be aiming for do you think? I do not wish to raise the floor for a multitude or reasons which arent relevant at the moment, so the spreader plate is the only option at the moment. 

 

The whole purpose of insulating the floor is to stop the downwards loss of heat, and im trying to address that to the best of my knowledge. If what ive suggested wont work, what would be the best solution?

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3 hours ago, Edward said:

Ok thanks for the reply.

 

I dont have any plans yet. Yes the floor is in, the house was built in the 30s. Its my kitchen floor, and the depth of the space underneath the floor is enough to stand up in. The u value of 0.25, as far as im aware, is the U value which new builds are required to achieve. What u value should i be aiming for do you think? I do not wish to raise the floor for a multitude or reasons which arent relevant at the moment, so the spreader plate is the only option at the moment. 

 

The whole purpose of insulating the floor is to stop the downwards loss of heat, and im trying to address that to the best of my knowledge. If what ive suggested wont work, what would be the best solution?

If you don,t like the spray foam solution then just pack it all with insulation and  board the underside to make it air tight 

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Thanks Scottishjohn. I think on second thoughts it would be easier if i get a contractor to quote for the spray foam as you suggested. 

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1 hour ago, Edward said:

I think on second thoughts it would be easier if i get a contractor to quote for the spray foam as you suggested. 

Hi Edward.

The guys on here are striving to get the best solution, so they answer according to that ethos ;)  You're not doing anything "wrong" just there are ways to go about this which will yield better results. 

Infiltration will be the killer here, so you really need to stop the focus on insulation and look closely at draught-proofing, against the ventilation heat losses you will have with the cold ventilated void, and then you wont have to be so critical when the insulation dilemma gets decided.

Spray foam is a good way to address both issues, as long as the detailing is correct, so you need to ask the difference between open and closed cell foam and where they should be employed to make sure the timbers don't end up sweating. Ask about insect and vermin barriers also, as insulation is a friend of the tunnel bunnies.  

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My remaining suspended floors will be dug up then rebuilt back up with min 150mm pir and concrete slab with UFH. 

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21 hours ago, Edward said:

The u value of 0.25, as far as im aware, is the U value which new builds are required to achieve.


Welcome

 

That is a very poor level of insulation for floor - new build standard is 0.11 from memory. 
 

Can you get under the floor once the UFH has been laid..? This may change the approach to how things are installed and in which order. 

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7 hours ago, Onoff said:

My remaining suspended floors will be dug up then rebuilt back up with min 150mm pir and concrete slab with UFH. 

Bet you don't have "space underneath the floor is enough to stand up in" though!

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1 hour ago, PeterW said:


Welcome

 

That is a very poor level of insulation for floor - new build standard is 0.11 from memory. 
 

Can you get under the floor once the UFH has been laid..? This may change the approach to how things are installed and in which order. 

Yes, access to under the floor wont be compromised once the UFH has been laid. 

 

Nick, thank you. I understand the basic differences between closed and open cell foam.  Can you elaborate on what should be used where? Obviously avoiding the timbers sweating is important!

 

Thanks


Ed

 

 

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I would not use spray foam here as it’s overkill and not what it is designed to be used for. 
 

I would let the builder put the spreaders in, then re-lay the floor. Then from underneath fit rockwool tight under the pipes and compress it slightly by capping off under the rockwool with 50mm of PIR (Kingspan or Celotex) and then use battens screwed across the joists to hold it in place. 

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Posted (edited)
29 minutes ago, Edward said:

Nick, thank you. I understand the basic differences between closed and open cell foam.  Can you elaborate on what should be used where? Obviously avoiding the timbers sweating is important!

the main difference is closed cell is ,as it sounds a waterproof and air tight  barrier 

they don,t cover the beams totally they leave bottom edge un coated --beams breathe there

i don,t see sweating as a problem as you are closing off the damp under floor from the nice dry interior and the heating is on top of that -so sweating will not be a problem 

It has become a common product to use on the outside of a basement  wall to give both insulation and the dpc rather than tanking 

 

 OVERKILL--don,t agree -better  insulation and draft stopping abilities is what we all strive for 

price up the alternatives and then decide 

 

Edited by scottishjohn

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3 hours ago, pdf27 said:

Bet you don't have "space underneath the floor is enough to stand up in" though!

 

Didn't read that. In that case wine cellar/ red room / dungeon.

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Posted (edited)
12 hours ago, Nickfromwales said:

Ask about insect and vermin barriers also, as insulation is a friend of the tunnel bunnies. 

I have seen closed cell used in stables etc to stop the mositure from heat of horses and corrosive piss fumes  on under side of roof and to also glue the old roof together including sticking the slates in place  on an "english" style roof -no sarking boards -just batons to nail slates to -first saw it 20 years ago --the old roof is still up and looking as good as it did then 

 but never seen any holes in it from insects boring into to it

Edited by scottishjohn
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2 minutes ago, scottishjohn said:

I have seen closed cell used in stables etc to stop the mositure from heat of horses and corrosive piss fumes  on under side of roof and to also glue the old roof together including sticking the slates in place 

 but never seen any holes in it from insects boring into to it

Was more worried about rats / mice than insects TBH. And I assumed closed cell would be the weapon of choice, but I've no direct experience of the products, other than in a marine environment, so best the OP asks all the questions to the installer and that they get a warranty that reflects what they are told, re suitability and longevity. Have also seen it used on battered roofs with great results.  

I assume they will staple on some sort of fine nylon webbing / other to the underside of the joists to catch the liquid from falling down between them whilst the first lot expands / cures, so wondered if that may as well be a metal mesh first as last. Never seen one done in honesty so don't know exactly how they execute such an installation, maybe they just build it up in layers as the stuff does expand crazy quick.

 

Anybody?

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Posted (edited)
32 minutes ago, Nickfromwales said:

Was more worried about rats / mice than insects TBH. And I assumed closed cell would be the weapon of choice, but I've no direct experience of the products, other than in a marine environment, so best the OP asks all the questions to the installer and that they get a warranty that reflects what they are told, re suitability and longevity. Have also seen it used on battered roofs with great results.  

I assume they will staple on some sort of fine nylon webbing / other to the underside of the joists to catch the liquid from falling down between them whilst the first lot expands / cures, so wondered if that may as well be a metal mesh first as last. Never seen one done in honesty so don't know exactly how they execute such an installation, maybe they just build it up in layers as the stuff does expand crazy quick.

 

Anybody?

 as long as it dry it will just stick like shit to a blanket as soon as it leaves the gun it starts expanding  no real liquid

Edited by scottishjohn
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