Suspended Timber Floor insulation - critique my plans please.

[SoliD]

Hi, 

 

First post, but hopefully i'll be back for more having discovered this forum.

 

I've got a 1969 built Detached house, ground floor is standard of it's age cavity which has been filled at some point (looked to be in ok shape when I had some doors replaced, and first floor is tile hung single skin. About 2 years ago I started the process of IWI of the first floor with battens and 50mm celotex, which has massively improved the comfort of the floor, but now the ground floor needs some attention as it's generally quite cold, although this isn't helped by the 9x3.5m kitchen/diner only having one double radiator as it's heat source...

 

I have a suspended timber floor with typical 400mm joists, and below this about 30cm or so of space. My plan is to get the floorboards up and in the lounge and hallway insert 100mm PIR between the joists, tape everything up then relay floorboards or lay osb/chipboard depending upon the survival rate, and then in my kitchen/dining room I plan to add a wet UFH heating system to replace the lonely radiator. This will be 25mm dry screed between the joists, then 100mm PIR which i would batten the joists and then support from underneath, and then reading around adding another 100 or 150mm of EPS70 to the bottom of the PIR. 

 

Just wondering if i've missed anything or if I could possibly save some money doing similar another way.

[Super_Paulie]

as long as the EPS70 doesnt enclose in the bottom of the joists it'll be ok. The bottoms need to be left exposed to the air under there. See attached for what i have done in my own in terms of insulation, the lower 50mm is held on nails and the whole lot foamed and taped in.

So long as your UFH system and design is sound, i dont see any real issues. JohnMo and Nick on here will be along soon im imagine, i got most of my top quality info from them in terms of buffer tanks etc.

[SoliD]

yep, will be attached to the pir with joists free to breathe, did think about cross laying it and leaving occasional air gaps, but then crossed that off the list as a stupid idea, although not quite thought of how to attach it to the PIR yet, could I use some sort of grab adhesive like sticks like s***.  Up until yesterday it was just going to be 100mm PIR, until I read more and more about the importance of the insulation under UFH. 

 

Would it be worth adding EPS to the non UFH sections too as the cost uplift isn't huge and if i'm under there may as well get it done.

Edited February 14 by SoliD

[Super_Paulie]

i have my lower PIR attached by using clout nails into the battens and then pushing the 50mm into those nails so its held in that way, then foamed and taped. Then the 120mm over the top, staggering the joins and again foamed and taped.

Yeah, the more insulation the better as far as im concerned, i have mine over the entire ground floor no matter if it has UFH over it or not, such as under the kitchen and island units. 

[SoliD]

 Cool thanks, kitchen will be fun as units will obviously have to stay in place so a lot of crawling about...

[Super_Paulie]

@JohnMo is really clued up on this and might be able to advise you further.

[JohnMo]

Main things I would think about

 

Good insulation as the air below the floor is much colder than soil so losses downwards can be quite big. Especially if you heed the next thing 

 

The other is keeping the upward thermal resistance low. Otherwise the flow temperature though the loops can be very high to get through.

 

Another way to do the insulation is use a breather membrane and allow to droop between joists then add mineral wool. Can see two clear advantages, airtightness and getting a good smug fit of the insulation first time.

19 hours ago, SoliD said:

wet UFH heating system to replace the lonely radiator.

Then just replace the floor boards and utilise your existing radiator or replace with a designer one. Way cheaper to run, system inertia matches the rest of the system. No additional pump to run, home to find for a manifold.

[Super_Paulie]

my "backup" radiators are the classical style i guess you'd call them, raw triple column and the heat they give out and retain compared to your standard radiator (that i have elsewhere) is unreal. They stay warm for hours afterwards when the others are stone cold.
 

29 minutes ago, JohnMo said:

The other is keeping the upward thermal resistance low. Otherwise the flow temperature though the loops can be very high to get through.

I have 22mm chipboard in mine which leaves me nervous for when i finally get round to commissioning it. If i could go back id defo get 18mm or a cement board of sorts but im all in now with the chipboard.
 

[SoliD]

Thanks. sorry the lonely radiator is not capable of putting out enough heat for the kitchen and dining room no matter how much it's insulated, it's a 9m long space... well planned by the previous owners. Despite putting a larger double rad which is 1.5m long from memory. There is no space in the kitchen area which is 6m of this length to put a rad as it's all cupboards, hence the move to UFH. 

 

Will ensure to minimise the resistance upwards, would be looking 18mm osb/chipboard with lvt on top, so minimal TOG rating.

[Super_Paulie]

i have 2 large rads and 2 plinth heaters in my large space (70sqm) as a backup for the UFH. Those plinth heaters really chuck out some heat, might be worth looking at if you have a lot of kitchen units.

[SoliD]

Started getting the floor up in the lounge. The concrete base here is no way near as deep as where I measured in the understairs cupboard, so i've got about 170mm under the joists to play with. Will get this tidied up and make a start on this half of the room tonight with some luck (depending upon how helpful the wife is with the clearing up )

Edited February 27 by SoliD

[joe90]

Will you need UFH with all that insulation? Whilst the floor is up you could double the size of that radiator easily (cheaply) and/or run pipes to fit a plinth heater in your kitchen. As @JohnMo says UFH requires way more kit to be installed.

[SoliD]

This is the lounge, not putting in UFH here. UFH is only going in the kitchen room, am considering plinth heaters, but had them before and as nice as the blowing warm air is, there is the additional comfort element that UFH provides.

Edited February 27 by SoliD

[SoliD]

got half the lounge done and back together now, measuring 1c warmer on the insulated sides carpet currently, now to crack on and do the other half. 

 

Bit faffy, but unfortunately limited on space to move furniture due to a 3 month old puppy, although her barking at me sat on the joists was pretty funny , looked at the taped up celotex with quite a lot of scepticism  

[SoliD]

Lounge all done, got quicker on the second half in terms of time taken, had a couple of iffy celotex cuts, which at the end of a day annoys the hell out of you with ropey joist widths  Just need to put some foam in a couple of plug and light sockets and room to go back to normal. Started pulling up a couple of laminate boards in the hallway now, looks like owners have boarded this when they had it done, so hopefully be a lot quicker than taking up and putting the floorboards back in the lounge. Will see how the room feels in the next few days, but with some of the knot holes in the floorboards, it's not hard to see why the room leaked heat on a windy day.