Suspended Floor UFH Dilemma

[JulianB]

Morning All,

 

I'm aware that this topic has been covered quite abit over the years (sorry!), however I've still got a few unanswered questions for my particular application...

 

We're in the process of building an upside down extension (i.e. living space upstairs), and are planning to install UFH throughout (through ASHP). All the heat loss calcs check out.

 

With respect to the first floor build up, we were initially going down the 'Torfloor' or similar option i.e. a routed structural board, which we would then cover over with engineered wood flooring. PIR insulation would be installed on the underside between each Easi Joist. This decision was primarily driven by not having a generous amount of head height at first floor level (just shy of 2m at the perimeter, with a vaulted 45 degree ceiling).

 

We are now expecting delays on the oak roof trusses and hence the first floor is likely to be exposed to the elements for a longer period of time than expected, at the wrong time of the year...

 

Seeing as most routed chip boards are not weather resistant in the slightest, our options are either to temporarily board the floor (spare ply boards etc) together with DPC to (hopefully) protect the joists, OR go down the route of using a weather resistant 'plain' permanent floor board at this stage, and later on down the line install a routed (non structural) insulation board to lay the UFH pipes, ultimately raising the FFL by ~20mm. The upside of the latter option would be that we could potentially get cracking with the floor now (and only do it once), giving us a solid platform to work off as we continue to build up walls and eventually install roof trusses and what not. The natural negative is the floor height, however I've wondering whether the fact that the UFH is now encased in insulation rather than for example the TorFloor chipboard, would actually make it perform better as it is not directly in contact with the floor joists.

 

My final query is 'just how important is insulation between first floor joists' when the floor is technically within the thermal envelope of the building. Would there be a valid argument that the whole floor would become a heat sink and continue to function fairly efficiently, or would the losses to the perimeter wall within the floor joist depth be far too great to make any sense?

 

Any comments / advice would be much appreciated!

[scottishjohn]

14 minutes ago, JulianB said:

go down the route of using a weather resistant 'plain' permanent floor board at this stage, and later on down the line install a routed

 or just route that floor later 

 this is what i did 20 +years  ago --no  pre routed board existed then 

 1/2" route and very good extraction -the trend system is first class 

and you will probably use 2 or 3 router bits  or more if you don,t move screws ro miss your tracks ,before you start-guess how I know .LOL,only my floor was nailed then --what a bitch 

 made up a template to go round corners at each end of run 

 

my channel was 30mm wide and 10mm deep as it was a triple pipe system - --modern type will be deeper but narrower

 i finish off by glueing and screwing 6mm ply on top of flooring to put back the strength 

 

[PeterW]

2m at the eaves is more than adequate so losing 20mm is nothing. You also need to consider that for an easy joist type system, the boards are glued to the joists to make the whole structure stronger. Pre-routed boards wouldn’t do that as well, and would also fill full of crap and rubbish such as plaster if the pipes were not immediately laid and then you would need a covering - either temporary or permanent - before you could continue. 
 

I would be using an overlay system and also getting insulation under the main boards for both sound and heat insulation - you want the heat upward ..!

 

Have you discounted using one of the spreader plate systems under a standard floor..?

[JulianB]

10 minutes ago, scottishjohn said:

 or just route that floor later 

 this is what i did 20 +years  ago --no  pre routed board existed then 

 1/2" route and very good extraction -the trend system is first class 

and you will probably use 2 or 3 router bits  or more if you don,t move screws ro miss your tracks ,before you start-guess how I know .LOL,only my floor was nailed then --what a bitch 

 made up a template to go round corners at each end of run 

 

my channel was 30mm wide and 10mm deep as it was a triple pipe system - --modern type will be deeper but narrower

 i finish off by glueing and screwing 6mm ply on top of flooring to put back the strength 

 

 

Thanks for the advice, sounds like a good route to go down (drum roll!). How long did it take you to get through that job??

 

 

5 minutes ago, PeterW said:

2m at the eaves is more than adequate so losing 20mm is nothing. You also need to consider that for an easy joist type system, the boards are glued to the joists to make the whole structure stronger. Pre-routed boards wouldn’t do that as well, and would also fill full of crap and rubbish such as plaster if the pipes were not immediately laid and then you would need a covering - either temporary or permanent - before you could continue. 
 

I would be using an overlay system and also getting insulation under the main boards for both sound and heat insulation - you want the heat upward ..!

 

Have you discounted using one of the spreader plate systems under a standard floor..?

 

I wasn't aware of the need to glue the boards to the joists, thanks for that! Re. spreader plates, I wasn't too keen on them as I couldn't imagine insulating the underside with PIR without leaving considerable gaps given their profile (unless I were to use some sort of spray foam?). The routed board option does give you a nice smooth surface to work with on the underside

 

[willbish]

47 minutes ago, JulianB said:

our options are either to temporarily board the floor (spare ply boards etc) together with DPC to (hopefully) protect the joists

 

I used second hand site hoardings, painted sheets of OSB, from a fencing supplier as a temporary deck through the winter. No need for DPM to protect the joists, they were unaffected.

 

Sheets were £6 a pop and can we sold on

[PeterW]

22 minutes ago, JulianB said:

 

I wasn't aware of the need to glue the boards to the joists, thanks for that! Re. spreader plates, I wasn't too keen on them as I couldn't imagine insulating the underside with PIR without leaving considerable gaps given their profile (unless I were to use some sort of spray foam?). The routed board option does give you a nice smooth surface to work with on the underside

 

Why PIR..?? Just pack the cavity with fibre insulation as that’s better for sound reduction and easier to put around cables and pipes that will be running through the space. 
 

Have to say, the routed boards seem (an expensive) solution looking for a problem. 
 

If you have standard width rooms at say 3.5m, a 45 pitch will give you a ceiling height of over 5m at the apex, you won’t notice if the outer wall is 2m or 1.95m ..!

[scottishjohn]

21 minutes ago, JulianB said:

Thanks for the advice, sounds like a good route to go down (drum roll!). How long did it take you to get through that job??

as it was house i was living in it will be a guess but about a day per room  even the kids got involved -screwing down the 6mm over ply 

 the question you should be asking is would I do it  that way again  now 

no

If  i had enough space to sliding widows and doors etc _i would  use a layover system 

and shorten doors etc would be quicker and insulation is built into the boards on some systems

 but next time i get involved with UFH it will be a new build  not a refurbishment 

 

[Temp]

What is your overall floor thickness? We opted for a beam and block first floor.

[willbish]

1 hour ago, PeterW said:

 

Have to say, the routed boards seem (an expensive) solution looking for a problem. 

Yeh I agree. The big advantage of them is avoiding the messing around involved with feeding pipe through the webs of posi joists where you can't notch them out.

 

A job I've not completed yet but fills me with dread every time i think of it!

[JulianB]

3 hours ago, PeterW said:

Why PIR..?? Just pack the cavity with fibre insulation as that’s better for sound reduction and easier to put around cables and pipes that will be running through the space. 
 

Have to say, the routed boards seem (an expensive) solution looking for a problem. 
 

If you have standard width rooms at say 3.5m, a 45 pitch will give you a ceiling height of over 5m at the apex, you won’t notice if the outer wall is 2m or 1.95m ..!

 

Yeah I see your point re. opting for fibre insulation - my only concern is whether over time the fibre will compress / sag and you end up with an air gap to the underside of the floor. PIR gives you a little more structural rigidity?

 

3 hours ago, scottishjohn said:

as it was house i was living in it will be a guess but about a day per room  even the kids got involved -screwing down the 6mm over ply 

 the question you should be asking is would I do it  that way again  now 

no

If  i had enough space to sliding widows and doors etc _i would  use a layover system 

and shorten doors etc would be quicker and insulation is built into the boards on some systems

 but next time i get involved with UFH it will be a new build  not a refurbishment 

 

 

Thanks; will definitely keep that in mind!

 

 

3 hours ago, Temp said:

What is your overall floor thickness? We opted for a beam and block first floor.

 

Floor joist depth is 220mm; not sure if our first floor would support beam and block seeing as our inner leaf is constructed out of the 2.9N blocks?

 

2 hours ago, willbish said:

Yeh I agree. The big advantage of them is avoiding the messing around involved with feeding pipe through the webs of posi joists where you can't notch them out.

 

A job I've not completed yet but fills me with dread every time i think of it!

 

Good luck! I came across a few examples of people threading them through the webs - are you concerned at all about the length of pipe that will be submerged in your floor and not in contact with the underside of the floor?