Great idea or terrible UFH retrofit idea

[jayroc2k]

I have just 70mm joists on sleeper walls in a victorian house, I can just about add at least 50mm celotex once they have been battened. This leaves me with the following solutions

- Expensive- re joist the floor to accept spreader plates (irregular spacings), then 21mm structural plywood/chipboard and 11mm Chevron (lady is set on them)

- tongue and grooved board with 12mm pipe, this requires 6mm ply glued on top for rigidity then chevron on top

 

and my light bulb idea

- 50mm celotex between joists

- use existing original floorboards but space them (gaps) by about 15-16mm,

- laydown singe run spreader plates for 15mm pipes

- 6mm backer board on top as this will be less insulating, add a heat sink and allows for the chevron wood to be glues on top

- lay the engineered chevron on top

 

what could go wrong? no need to buy grooved boards... i feel i have missed something big here

 

BTW - neighbour put underfloor heating under original solid floorboards 8 years ago and they have not warped.

[Crofter]

I have no experience of this sort of project at all but it sounds interesting.

So you would take up all the existing floorboards and work from above- how would you keep the PIR in place? Little 20mm battens running along the bottom edge of each joist perhaps?

You will possibly lose some strength/rigidity when you space out the (T&G?) boards.

Will be interesting to see what other people say.

[Nickfromwales]

Ventilation heat loss from below the floor will be a big factor. How much space is there between the underside of the joists to the ground? 

50mm of cellotex / similar will be quite inadequate imho. 

Draughtproofing the insulated envelope ( NOT the ventilated void underneath ) will be of paramount importance. 

Can you not remove and backfill with insulation and concrete / screed?

[Ferdinand]

1 hour ago, Crofter said:

I have no experience of this sort of project at all but it sounds interesting.

So you would take up all the existing floorboards and work from above- how would you keep the PIR in place? Little 20mm battens running along the bottom edge of each joist perhaps?

You will possibly lose some strength/rigidity when you space out the (T&G?) boards.

Will be interesting to see what other people say.

 

I thought the other approach here was to line the void with a damp proof something to keep it dry and fill it entirely with polystyrene beads like a beanbag, then no need for PIR pfaffing. Possibly with a french drain added at foundation level outside to make sure it stayed dry. There are probably other details.

 

I think that the approach proposed by Jayrock is quite normal but rather a lot of work, and you need to worry about doors, proportions, ceiling height etc.

 

Ferdinand

 

Edited October 10, 2016 by Ferdinand

[ProDave]

 

i share the concern that 50mm is not enough insulation. You need to get some more insulation UNDER the existing joists as well as in between them.
 

[Nickfromwales]

3 hours ago, Ferdinand said:

 

I thought the other approach here was to line the void with a damp proof something to keep it dry and fill it entirely with polystyrene beads like a beanbag, then no need for PIR pfaffing. Possibly with a french drain added at foundation level outside to make sure it stayed dry. There are probably other details.

 

I think that the approach proposed by Jayrock is quite normal but rather a lot of work, and you need to worry about doors, proportions, ceiling height etc.

 

Ferdinand

 

Will that be wise if it's a ventilated void?

[Barney12]

We did something similar in a refurb a few years ago. You don't state how big the void below the floor is but we had enough to crawl under.

We attached two battens to opposing walls. We then stapled pallet banding between the battens and then sandwiched another over the top to hold the strapping tight.

We then laid 200mm of loft insulation on top of it tight up to the bottom of the joists. Then 50mm celotex between the joists.

This didn't compromise the air bricks and left a good level of ventilation below the floor.

There was no real way of knowing exactly how effective it was but the house was warm and draft free.

 

 

[Ferdinand]

1 hour ago, Nickfromwales said:

Will that be wise if it's a ventilated void?

 

It won't be a void any more so you take the ventilation away / block it up and make sure it stays dry to prevent rot.

 

There have been rather extensive discussions on this idea at the other place going back to about 2011, so I would suggest some reading over there, and quie a few houses done.

 

@SteamyTea has a longer history than me there, and may have a better State of the Debate perspective.

 

This is the most recent thread I can find but debates on GBF are a little like a querulous MENSA dinner in a pub sometimes, but very illuminating. You may want to read others too.

http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13524&page=1

 

If it was me I would fill the insulation to the top or nearly the top probably with a liner if possible, blocked up the ventilation, put in a perimeter French drain at the bottom of a trench outside, filled the trench with LECA for coldspots (or gravel) and the top 6" with pea gravel, then loose lay 3'x2' Council Slabs on top as a path so I can get to it all if I needed to maintain it. Even better, combine it with EWI. 

 

The outside works could probably be done in bits.

 

There would be a case for leaving a small void at the top for electric cables etc as they may degrade over decades in contact with polystyrene balls (I am told).

 

I would first have checked that this was all above the water table all of the time.

 

You also learn to be good with a minidigger by digging a trench 1" from your house all the way round without destroying it. Surprisingly easy to do.

 

Ferdinand

 

Edited October 10, 2016 by Ferdinand

[SteamyTea]

1 hour ago, Ferdinand said:

has a longer history than me there, and may have a better State of the Debate perspective.

I agree with Mike George (I think).

All I do is work out the chance and frequency of hitting a dew point condition and use that to calculate a risk.

 

Trouble starts when you take data from one place (say the gap between my roof and the extra insulation on my rafters) and transferring it to someone else roof.  They may not have the same orientation, weather or climate. I have a very moderate climate, only two seasons really (my winter is like early spring or late autumn, summer is like a late spring or early autumn) , very strong winds (at any time of year) that hit my house side one, so nip up into my roof nicely.  I have higher than normal insolation (for the UK), but in a more spasmodic manner.  Higher RH levels but very really cold enough to hit the dew point.

[jayroc2k]

I intend to leave the void underneath the joist for ventilation. I can get in 70mm PIR by using netting/quilt blanket instead battens, it will look similar to the photo here

http://javitas.info/image.php?pic=http://constructionstudiesq1.weebly.com/uploads/1/6/4/9/16490624/1364413461.png

 

This single spreader plate will sit on two normal period floor boards spaced to allow the groved part sit in the gap (pink bit are floor boards, black bits are joists under neath), the spreader plates sit on top, not under as it looks in the pic

 

a backer boark like this to glue down the chevron flooring as would not want to glue to the original flooring, 

 

http://www.theunderfloorheatingstore.com/prowarm-backer-pro-tile-backer-board?

 

Edited October 10, 2016 by jayroc2k
clarification

[Crofter]

What are the joist spacings, board thickness, board width? I'd just be a bit worried that without being locked together tongue & groove, they might deflect and move too much.

[Nickfromwales]

You won't be using those boards 

 

Experpt.....

"

ProWarm™ BACKER-PRO insulation Boards are ideal for two primary purposes; as a superior waterproof surface to fix wall or floor tiles and as a first class heat insulation for underfloor heating systems.

ProWarm™ BACKER-PRO insulation boards are particularly suited to underfloor and under tile heating applications. Installation below underfloor heating systems on an existing un-insulated concrete or timber sub-floor will greatly reduce heat up time and running costs."

Youd be better off with a quality plywood, but I'd probably recommend that you fix engineered flooring directly over the plates. I'd bond them down rather than mechanical fix or floating, so they have a good contact for heat transfer but still some movement. 

[jayroc2k]

Board thickness is 21-22mm, they are the board found in any old Victorian home, nailed to the floor joists 

[Nickfromwales]

4 hours ago, Crofter said:

What are the joist spacings, board thickness, board width? I'd just be a bit worried that without being locked together tongue & groove, they might deflect and move too much.

You'll find they'll be well seasoned by now and take a lot of 'abuse' eg having Ufh. I'd favour that existing timber over new stuff all day long. .