Float or glue engineered flooring over chipboard with UFH

[gOBO81]

Our extension build is nearing completion and it's time to lay the flooring; around 60m2.

 

It is a suspended timber joist floor with spreader plates and wet UFH piping throughout. Laid on top of the joists is 18mm chipboard.

 

We have selected to lay a 14mm engineered flooring (3mm oak top layer). We would prefer to have this glued down but our builder has suggested it would likely have to be floated due to the UFH expansion/contraction.

 

I am struggling to find clear guidance on glueing down as most guidance appears to presume where there is UFH it is screeded, but we have a suspended floor.

 

If anyone could offer any advice it would be greatly appreciated.

 

Cheers

[Mr Punter]

Glued will feel more solid but either will do.  Either way, leave a decent expansion gap around the perimeter.

[JohnMo]

  On 27/09/2024 at 16:19, gOBO81 said:

am struggling to find clear guidance

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Flooring manufacturer instructions normally give explicit instructions. Ours had to be glued down on top of UFH. Doesn't mean yours will. If in doubt ask the supplier.

 

 

 

 

[joe90]

  On 27/09/2024 at 16:29, Mr Punter said:

Glued will feel more solid but either will do.  Either way, leave a decent expansion gap around the perimeter.

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+1, I hate floating floors. Plus the glue will help transfer the heat better.

[gOBO81]

  On 27/09/2024 at 17:19, joe90 said:

+1, I hate floating floors. Plus the glue will help transfer the heat better.

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Likewise, hence it being our preferred method. 

 

Is there a particular glue that is preferred for adhering to chipboard floors? I presume it would need to be flexible? 

[joe90]

The flooring supplier usually recommend/stipulate the best adhesive (ours did).

[Mr Punter]

  On 27/09/2024 at 17:23, gOBO81 said:

Is there a particular glue that is preferred for adhering to chipboard floors? I presume it would need to be flexible? 

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It is very expensive.  Essential that the subfloor is completely dust free, which is difficult to maintain unless you do the cutting remotely or with a posh Festool thing.

[joe90]

  On 27/09/2024 at 17:54, Mr Punter said:

 

It is very expensive.  Essential that the subfloor is completely dust free, which is difficult to maintain unless you do the cutting remotely or with a posh Festool thing.

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Yes my glue (can’t remember the  type) was pricey. Also I vacuumed each bit of floor just before laying down the glue to make sure it was dust free.

[Gus Potter]

  On 27/09/2024 at 16:19, gOBO81 said:

Our extension build is nearing completion and it's time to lay the flooring; around 60m2.

 

It is a suspended timber joist floor with spreader plates and wet UFH piping throughout. Laid on top of the joists is 18mm chipboard.

 

We have selected to lay a 14mm engineered flooring (3mm oak top layer). We would prefer to have this glued down but our builder has suggested it would likely have to be floated due to the UFH expansion/contraction.

 

I am struggling to find clear guidance on glueing down as most guidance appears to presume where there is UFH it is screeded, but we have a suspended floor.

 

If anyone could offer any advice it would be greatly appreciated.

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It's a dilemma!

 

Over the years I've done a few UF systems and each time I learn something new, improve where I can and adapt the design the based on my learning and what new on the market.

 

The house we have at the moment is a 1955 house with suspended floors. We took the back off it and extended out to form an open plan space. The extension is a concrete slab on PIR on grade. But the floor levels in the existing house vary and as they are now forming part of the open plan space we have a mix of materials forming the floor. Timber / concrete and a level variation.. it's small but it is there. Also the existing house solum is sealed with tar and a bit compromised in places thus we have different moisture levels.

 

All of the above results in movement between winter and summer which is noticeable.. if you are inclined that way to have these thoughts. For this house I floated the engineered flooring on a 2.0mm thick layer of foam, just the bog standard stuff. If you jump about on the floor you are aware that the different parts feel more solid than others. But again I'm always "monitoring! most folk wonder if I'm ill when I mention. Now fair enough the foam insulates and makes the UF less quick to respond. In the odd spot where the floor levels were a bit off locally I added some extra strips of foam as a packer. But we have lots of rugs and so on which do insulate the floor much more so than a thin layer of foam. If you lift a rug the floor is much hotter under.

 

We have a bathroom on a supsended joisted floor. The tiles are these large format ones. The UF pipes are in a screed on PIR between the old house joists, no spreader plates. A while ago I posted about this and @nod as always provided some great advice. I followed it and sure enough after almost two heating seasonal cycles no cracks in the tiles. Thanks @nod! The main thing was the use of a decoupling matt. When I first started messing about with UF these products were not available.. mind you neither were large format tiles available to the DIY market at an affordable price.

 

Now when you read the fine print of the flooring suppliers you nearly always breach their T & C's in terms of what you need to comply with. One it the temperature range. Where you have UF pipe conjestion the floor can get quite hot at times cf other areas. I just accepted that is was nearly impossible to comply for our house so took a pragmatic risk based approach.

 

In summary I did think about glue the floor down. But then I though what happens if I get a leak in the kitchen sink say . Lifting any damage glued down flooring could be a nightmare! We have had a plant pot that leaked water and did not spot. Some minor damage has occurred but I know I can easily fix the floor if need be.

 

 

 

 

 

 

 

[nod]

  On 27/09/2024 at 18:31, Gus Potter said:

It's a dilemma!

 

Over the years I've done a few UF systems and each time I learn something new, improve where I can and adapt the design the based on my learning and what new on the market.

 

The house we have at the moment is a 1955 house with suspended floors. We took the back off it and extended out to form an open plan space. The extension is a concrete slab on PIR on grade. But the floor levels in the existing house vary and as they are now forming part of the open plan space we have a mix of materials forming the floor. Timber / concrete and a level variation.. it's small but it is there. Also the existing house solum is sealed with tar and a bit compromised in places thus we have different moisture levels.

 

All of the above results in movement between winter and summer which is noticeable.. if you are inclined that way to have these thoughts. For this house I floated the engineered flooring on a 2.0mm thick layer of foam, just the bog standard stuff. If you jump about on the floor you are aware that the different parts feel more solid than others. But again I'm always "monitoring! most folk wonder if I'm ill when I mention. Now fair enough the foam insulates and makes the UF less quick to respond. In the odd spot where the floor levels were a bit off locally I added some extra strips of foam as a packer. But we have lots of rugs and so on which do insulate the floor much more so than a thin layer of foam. If you lift a rug the floor is much hotter under.

 

We have a bathroom on a supsended joisted floor. The tiles are these large format ones. The UF pipes are in a screed on PIR between the old house joists, no spreader plates. A while ago I posted about this and @nod as always provided some great advice. I followed it and sure enough after almost two heating seasonal cycles no cracks in the tiles. Thanks @nod! The main thing was the use of a decoupling matt. When I first started messing about with UF these products were not available.. mind you neither were large format tiles available to the DIY market at an affordable price.

 

Now when you read the fine print of the flooring suppliers you nearly always breach their T & C's in terms of what you need to comply with. One it the temperature range. Where you have UF pipe conjestion the floor can get quite hot at times cf other areas. I just accepted that is was nearly impossible to comply for our house so took a pragmatic risk based approach.

 

In summary I did think about glue the floor down. But then I though what happens if I get a leak in the kitchen sink say . Lifting any damage glued down flooring could be a nightmare! We have had a plant pot that leaked water and did not spot. Some minor damage has occurred but I know I can easily fix the floor if need be.

 

 

 

 

 

 

 

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Your welcome 

[Gus Potter]

  On 27/09/2024 at 21:08, nod said:

Your welcome 

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I'll post a photo at some point so you can see where you advice was implemented! Thanks again. Do you want to come up and work in the Glasgow area?

[SteamyTea]

I think a wooden floor/laminate should be treated like a carpet, of the very reason that @Gus Potter says, you may need to remove it.

UFH complicates this, but I am sure there are 'underlays' that have high thermal conductivity.  A polypropylene ones maybe.

[Nickfromwales]

  On 27/09/2024 at 17:23, gOBO81 said:

Likewise, hence it being our preferred method. 

 

Is there a particular glue that is preferred for adhering to chipboard floors? I presume it would need to be flexible? 

Expand  

You need to be asking the supplier / manufacturer, and explaining the floor construction / UFH situation to get the correct technical advice. This then needs to be conveyed to your heating installer to make sure there is a strategy for preventing the flow temp ever exceeding the max allowable temp (usually 27oC).

 

As for floating the floor, don’t even dream about that, the UFH will 1000% need this to be bonded down if it is the only means of providing space heating. Also, have you calculated the room heat loss vs what the floor is likely to emit (heat-wise) per m2 as there are a lot of disappointed UFH owners out there who haven’t  

Edited September 30, 2024 by Nickfromwales
typo

[Gus Potter]

  On 29/09/2024 at 23:48, Nickfromwales said:

You need to be asking the supplier / manufacturer, and explaining the floor construction / UFH situation to get the correct technical advice. This then needs to be conveyed to your heating installer to make sure there is a strategy for preventing the flow temp ever exceeding the max allowable temp (usually 27oC).

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Agree with Nick here.. but..

 

  On 29/09/2024 at 23:48, Nickfromwales said:

As for floating the floor, don’t even dream about that, the UFH will 1000% need this to be bonded down if it is the only means of providing space heating. Also, have you calculated the room heat loss vs what the floor is likely to emit (heat-wise) per m2 as there are a lot of disappointed UFH owners out there who haven’t

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Here lies the problem as I mentioned in my earlier posts. In my own case you just don't get to have you cake and eat it. Designing stuff is my day job so its easier for me to get my head around it.

 

I recognised that I have a big open plan floor that extends over different substructures that all move about differentially quite a lot. To compensate I over designed the UF in terms of pipe spacing close to the exposed perimeter of the building. The thermal conductivy is not as efficient when retrofitting to timber joists with screed  / insulation between . Each different element, concrete slab / suspended floor has got its own UF pipe loop so I could muck about with it.. cool parts if need be and so on. However the extended part of the house is exposed to the weather. In the concrete slab near the big bits of external glazing I decreased the pipe spacing.  The timber suspended floor has little exposed perimeter and thus it needs less "poke" from the UF.

 

At the end of the day I use my own engineering judgement (how materials behave) and past experience ( have done a few UF self builds / extensions) to put something together that works well. Could I prove this by calculation.. no chance without expending some 5- 10 k design effort producing some meaningless thermal model. I also pinched design principles from some of the industrial building I've designed over the years so this gave me confidence.

 

In summary.. I would put together your requirements and ask all the folk that need to contribute to the design.. look at their fine print.. and you may eventually conclude that with say a refurb / extension you need to take some extra risk as each supplier will put so many caveats on things you can't make them all meet in the middle. I mitigated this by practical and common sense design and some careful but practical drawing detailing.

 

 

 

 

[Nickfromwales]

Sadly, yes, as if you ask 5 different plumbers you'll likely get 5 different answers that each party swears by. I just go on 3 decades of doing "what feels right" and the confidence that it all worked well (or very well), as I tend to over-engineer a little for 'Justin' but the results always speak volumes.