Underfloor Heating

J_Smotthies2021

Hi,

I have a suspended ground floor with 50cm void space and would like to get underfloor done. Is that possible? If so how? 

It is a 1900ish old house.

thanks

grumbler

It is possible. First you have to add good insulation between the joists. Then there are various options. The simplest one is, possibly, plastic pipes with aluminium  spreaders between the joists under the floorboards.

- some random pictures from the internet.

J_Smotthies2021

thank you, My builder is saying that aluminium plates are not effective... He wants to remove the joists and fill in the void area with screed on top of insulation and to normal wet installation of the underfloor heating. I am not convinced on this. I believe screed might expand when heated and can push the walls of the house right? This is an old house and I wanna make sure that we do not create issues while installing the underfloor heating system

grumbler

J_Smotthies2021 said:

He wants to remove the joists and fill in the void area with screed on top of insulation and to normal wet installation of the underfloor heating. I am not convinced on this.

Neither am I. Filling 50cm space?!  Multiply this by the area and calculate the volume. Not to mention that it's a valuable space to lose.

Yes, it's possibly less effective, but works. And has a very low thermal inertia - unlike with screed. With the latter you are effectively heating a huge lump of concrete, about 1 cubic meter for an average room. I takes time to heat it in the morning and time to cool at night.

And I don't see how  warm screed under wooden floor is better than warm aluminium in the same place.

J_Smotthies2021

You are right, metal looks like a better option. I am not fully sure either what will happen if he fills all those space with screed/concrete etc. 

Do you think, I should still keep the radiators on the ground floor considering the low performance of the aluminium sheet solution?

grumbler

I don't know. IMO, the only point of heated wooden floor is to get rid of radiators. Unlike tiles, if insulated well, it's warm enough even without underfloor heating.

FreeBear

Chances are, the floor joists are 3"x2" timbers resting on dwarf walls - This is going to limit the amount of insulation that can be fitted between the joists without disrupting air flow. With suspended floors, you must have a certain amount of air circulating to prevent the buildup of damp and stop rot from setinng in.

If you (or your builder) are contemplating replacing the flooring with a concrete slab, be aware that building regulations will most likely apply. With a ~1900s property, your footings may not be deep enough to allow for sufficient material to be excavated in order to do a "proper job".

fenwick458

what stage is the house at, is it gutted and in the middle of major renovations, or fully furnished and you're living in it?
how many rooms and how many m2 are we talking about here?
what are you planning on putting on top of the heated floor? porcelain tiles, vinyl tiles, wood...?

Rosa_Damascena

J_Smotthies2021 said:

thank you, My builder is saying that aluminium plates are not effective... He wants to remove the joists and fill in the void area with screed on top of insulation and to normal wet installation of the underfloor heating. I am not convinced on this. I believe screed might expand when heated and can push the walls of the house right? This is an old house and I wanna make sure that we do not create issues while installing the underfloor heating system

That's what I'm having done BUT it's because I need the floors levelled. They are being fully gutted as part of a much wider project with wet UFH and new flooring. I have no concerns about screed expanding but accept it takes time to dry completely before floor can be laid down on it.

Doozergirl

I'm never a fan of underfloor heating in older houses unless you are also upgrading the insulation value of the entire house. 

Underfloor hearing relies heavily on the lower level of heat it provides being retained by the house for a start.  The house will never get warm if it's draughty.  Thing is, that the house needs a certain level of draught to prevent damp and condensation.     

Older houses have cold spots around windows, particularly, and radiators work in many cases to cover those cold spots.   Underfloor heating produces an ambient heat that you don't feel - it cannot cover cold spots.   

It's an expensive product - you want it to work correctly!  

J_Smotthies2021

It is a 5 bed house but on the ground floor we have a large reception 8.3m X 3.6m, and a large kitchen dining area which is 4m X 6.5m and a hallway. All ground floor will be renovated with a new kitchen so on.

I prefer laminate wooden floor in all areas including kitchen. 

My builder is not suggesting to replace the wooden floor with concrete slab. He is referring to screed only so heating works properly. Having said that he also said that he needs to remove the flooring first to see how deep it actually is.