Seeking advice on UFH in a 1940-1950 bungalow

[swank23]

Context - we recently purchased a 4 bedroom Bungalow with a top and rear extension. It is a 1940-1950 build with suspended timber flooring and solid walls. The rear extension kitchen was done in the last five years and is concrete flooring. The upstairs is also done in the last five year , so has cavity stud walls and better insulation. All windows are double glazed.

We are looking to renovate our ground floor and one thing we want to do is get underfloor heating. Our builder recommended that we can either go for spreader plate system or a pregrooved insulation board of 25mm

I was hoping to get everyone's guidance with the following:

1. Will the levels of floor insulations you would expect from a 1950 house, is it a good idea to go with underfloor heating with the above mentioned systems? Because if we have to redo the entire flooring to upgrade insulation, it would become quite expensive

2. I talked to one of the build regs inspector. They mentioned that the highest specification of regs are very high specification, but realistically they dont expect it can be always done during renovating, so they are flexible on what can be done. So I am hoping building regs wont be an issue, any thoughts

3. Is any one of the above systems better than other ? Are they situations when one is better than the other

4. Any thing we can do with flooring insulation which could be a quick win without massively increasing the height or cause redoing the sub floor

Thank you for your guidance.

[shalmaneser]

Getting some work done to our 1950's solid wall semi so interested to follow along here. Very keen on fitting UFH downstairs while we're getting all the work done.

[Lotobear]

You've two problems as I see it - 1) getting sufficient insulation into the existing floor to prevent a chunk of your heat disappearing into the sub floor void whilst also managing the increased risk of condensation in the sub floor and (2) getting sufficient thermal mass into your floor to act as the 'radiator' / heat sink

Whilst I'm sure it will have been done previously I would personally only consider it with a concrete floor construction where the pipes are laid/clipped over the insulation and the screed acts as the 'radiator'. It also sounds like a lot of work for what is likely to end up a compromise.

[shalmaneser]

Lotobear said:

You've two problems as I see it - 1) getting sufficient insulation into the existing floor to prevent a chunk of your heat disappearing into the sub floor void whilst also managing the increased risk of condensation in the sub floor and (2) getting sufficient thermal mass into your floor to act as the 'radiator' / heat sink

Whilst I'm sure it will have been done previously I would personally only consider it with a concrete floor construction where the pipes are laid/clipped over the insulation and the screed acts as the 'radiator'. It also sounds like a lot of work for what is likely to end up a compromise.

UFH on a suspended floor seems pretty common to me? Air is a pretty good insulator and heat rises so I'd assume that it would work better than on a slab which would require warming up and conduct heat downwards?

If you insulated between the joists you've got the best of both worlds? It does sound like a ball ache though.

[Lotobear]

shalmaneser said:

Lotobear said:

You've two problems as I see it - 1) getting sufficient insulation into the existing floor to prevent a chunk of your heat disappearing into the sub floor void whilst also managing the increased risk of condensation in the sub floor and (2) getting sufficient thermal mass into your floor to act as the 'radiator' / heat sink

Whilst I'm sure it will have been done previously I would personally only consider it with a concrete floor construction where the pipes are laid/clipped over the insulation and the screed acts as the 'radiator'. It also sounds like a lot of work for what is likely to end up a compromise.

UFH on a suspended floor seems pretty common to me? Air is a pretty good insulator and heat rises so I'd assume that it would work better than on a slab which would require warming up and conduct heat downwards?

If you insulated between the joists you've got the best of both worlds? It does sound like a ball ache though.

I follow your logic but it doesn't really work like that as whilst air does indeed provide a measure of insulation it needs to be still and by definition in a ventilated sub floor void you are going to, or should have, air movement and the air in it will be close to external temperature. Insulating between the joists can be done but introduces a risk of interstitial condensation and then leaves the intervening joists as thermal bridges. In an existing situation you can't go on top without messing up your internal heights

With a conventional slab UFH system you are not really heating the slab as it's fully isolated from the heating pipes by a layer of PIR insulation, circa 100mm thick - the pipes are laid on top and encapsulated in around 65mm screed with acts as the radiator. As I suggested UFH is a likely compromise with a suspended floor - you often have no choice upstairs but that's a different situation as there is no cold sub floor beneath.

[matty g]

1898 home here. We went with electric UFH due to suspended floor and ease. maybe an option for you?

[redexstyle]

We've just had underfloor heating fitted downstairs in our new home.

We didn't lose any height as we have a 1930's semi built with suspended floors. Old floorboards came up, 100mm insulation boards were fitted in between the joists, spreader plates on top and pipes fitted and then new 18mm floorboards so we're back upto the original level.

Would definitely recommend a spreader plate system for suspended floors.

I forgot to mention our kitchen is concrete so channels were cut to lay the pipes.

Hopefully this helps.

[swank23]

Lotobear said:

I follow your logic but it doesn't really work like that as whilst air does indeed provide a measure of insulation it needs to be still and by definition in a ventilated sub floor void you are going to, or should have, air movement and the air in it will be close to external temperature. Insulating between the joists can be done but introduces a risk of interstitial condensation and then leaves the intervening joists as thermal bridges. In an existing situation you can't go on top without messing up your internal heights

With a conventional slab UFH system you are not really heating the slab as it's fully isolated from the heating pipes by a layer of PIR insulation, circa 100mm thick - the pipes are laid on top and encapsulated in around 65mm screed with acts as the radiator. As I suggested UFH is a likely compromise with a suspended floor - you often have no choice upstairs but that's a different situation as there is no cold sub floor beneath.

Thank you this is helpful. if we can figure our insulation between joins without causing condensation issues, then is UFH still a bad choice. I know it is not going to as effective as concrete floor but is it still not good choice in terms of heating?

[swank23]

redexstyle said:

We've just had underfloor heating fitted downstairs in our new home.

We didn't lose any height as we have a 1930's semi built with suspended floors. Old floorboards came up, 100mm insulation boards were fitted in between the joists, spreader plates on top and pipes fitted and then new 18mm floorboards so we're back upto the original level.

Would definitely recommend a spreader plate system for suspended floors.

I forgot to mention our kitchen is concrete so channels were cut to lay the pipes.

Hopefully this helps.

Thank you for sharing your experience, this is very helpful. few questions:

1. Is the heating effective compared to traditional radiator heating? For example if temp falls below 2 Celsius, can this still help achieve over 20 internally

2. How has been the energy bills for same levels of heating, is it equivalent or more/less

[swank23]

matty g said:

1898 home here. We went with electric UFH due to suspended floor and ease. maybe an option for you?

Based on my research it is much more expensive to run and not effective in larger areas, so we are not considering it. Curious what are your energy bills for same level of perfornance compared to radiator

[Lotobear]

swank23 said:

Lotobear said:

I follow your logic but it doesn't really work like that as whilst air does indeed provide a measure of insulation it needs to be still and by definition in a ventilated sub floor void you are going to, or should have, air movement and the air in it will be close to external temperature. Insulating between the joists can be done but introduces a risk of interstitial condensation and then leaves the intervening joists as thermal bridges. In an existing situation you can't go on top without messing up your internal heights

With a conventional slab UFH system you are not really heating the slab as it's fully isolated from the heating pipes by a layer of PIR insulation, circa 100mm thick - the pipes are laid on top and encapsulated in around 65mm screed with acts as the radiator. As I suggested UFH is a likely compromise with a suspended floor - you often have no choice upstairs but that's a different situation as there is no cold sub floor beneath.

Thank you this is helpful. if we can figure our insulation between joins without causing condensation issues, then is UFH still a bad choice. I know it is not going to as effective as concrete floor but is it still not good choice in terms of heating?

Depends what you're trying to achieve really - do you want UFH as you are considering an ASHP or is it just something you would like? Personally, I would only really consdier it if I was starting from scratch as a new build or else a refurbishment where suspended floors were going to be replaced with concrete or a beam and block suspended floor and it could be designed 'holistically' (apologies, awful expression!). It's no more efficient than radiators but works well with low grade heat (such as via a heat pump system) where you need a large heat emitting surface.

But, in your situation it's a lot of work for little gain IMO

[swank23]

Lotobear said:

Depends what you're trying to achieve really - do you want UFH as you are considering an ASHP or is it just something you would like? Personally, I would only really consdier it if I was starting from scratch as a new build or else a refurbishment where suspended floors were going to be replaced with concrete or a beam and block suspended floor and it could be designed 'holistically' (apologies, awful expression!). It's no more efficient than radiators but works well with low grade heat (such as via a heat pump system) where you need a large heat emitting surface.

But, in your situation it's a lot of work for little gain IMO

Thank you for sharing. This is immensely helpful. We were considering UFH because there are a few narrow hallways where it is not possible to install radiators due to space constraints, also given our floor area in living and kitchen is limited, it would be great to not have radiators taking up space. Also my kitchen is concrete and living area is suspended timber floor, until we take out flooring we wouldnt know the state of insulation levels.

Based on your comments, I am seriously considering investing in UFH if it is going to have a poor ROI. There seems to be a lot of companies doing very well in selling multiple UFH products on timber flooring, not sure why there seems to be so much demand if this is not a successful solution.

Any recommendations on what we can do given our space constraints where we dont have cold spots in the house.

[Pheo]

For me retrofit UFH is a comfort thing.

I followed this guide in our 1930s place:

https://www.ecologicalbuildingsystems.com/post/bes...

The affect on the comfort level of the building has been truly transformative. Especially in the rooms with exposed floorboards of course!

We fitted UFH in spreader plates. Works well apart from the hallway - large space, old front door, single glazed window does mean the UFH does struggle to keep up a bit. In hindsight I’d probably have a backup radiator or consider the heat loss a bit better. Also doesn’t help it’s under chipboard there so that insulates it’s a bit. We put I think 50mm wool insulation in - I’d probably go for slightly more but didn’t want to compress it too much

UFH is a much nicer to be in so I prefer it hence doing it.

[redexstyle]

swank23 said:

Thank you for sharing your experience, this is very helpful. few questions:

1. Is the heating effective compared to traditional radiator heating? For example if temp falls below 2 Celsius, can this still help achieve over 20 internally

2. How has been the energy bills for same levels of heating, is it equivalent or more/less

1. We've not moved in yet but when we've been working in the house, the UFH has defo kept the warmth comfortable and lasted longer once turned off compared to how quick a radiator loses heat after turning off. We noticed the difference more so once we had insulated the ceilings. But already we're looking forward to our new heating experience. Give the downstairs has only just been boarded and plastered, we're not hitting the temperatures jus tyet as we have a couple of air gaps to sort plus no doors.

2. Not sure, we haven't compared yet but I'm due to log our next meter reading so maybe able to give guidance then. I know friends who have UFH have seen their bills come in lower than radiators.

Hope this helps.