Old pine floor boards and underfloor heating

[Alex F]

In my house I lifted the original pine floorboards and have installed underfloor wet system heating in a 70mm screed with 50mm of insulation under the screed. This is between new floor joists

A couple of people have warned against using these old pine boards with my underfloor heating due to the severity in the movement of the pine and ending up with a very gappy floor (like +5mm gaps)

I was proposing to stack the boards in the rooms with heating on for a couple of weeks before laying to allow the boards to adjust to the temperature change.

They have been stored in a dry but cold barn for about 5 months.

One chap suggested laying them on ply first but this would be an awful lot of work and I haven't allowed for this in the levels.

Any advice on this welcome. Thanks.

Alex

 

[AMc]

Our boards have been relaid over a piped radiator central heating system - by someone who took no account of expansion in the wood. When the heating comes on the sound of the boards moving and creaking wakes us up. This is something I am going to have to fix (somehow) and is something you will do well to avoid. I really hope I won't have to relay them completely and can strategically remove some fixings to let them move a little. I may need to expand the fixing holes so they can shift without splitting.

The ply idea sounds unnecessary and would surely insulate the heating lowering it's effectiveness and slowing it's response. While ply is more stable than pine, I would imagine it will move a little due to heat and moisture changes adding another possibility for your floor to flex unevenly.

Was the house centrally heated before as that would have dried the boards more than fires/stoves? You don't say how old your boards are - presumably they will have been gently drying out in the house for a long time before you removed them and letting them adjust from their storage in the barn sounds like a very sensible decision.

You've also put in new joists which are going to react to being warmed up too again potentially moving your new floor.

If it were me, I would begin heating the joists so they start to reach their target temperature and moisture levels before you bring in the boards (stacked) for a couple of weeks. Then if it's practical lay the boards without fixing to see how they react. If you find some warp then you can reposition them in less important places and you can get an idea of the amount of expansion you'll need to allow. It sounds like you'll need to take your time but I can't see why it shouldn't (eventually) work out OK.

 

[Alex F]

Thanks for your comments.

I am surprised the noise from the boards could be that loud from the heating going on and off.

The boards I have must be 100yrs old. The house was not centrally heated but was lived in and heated but not centrally.

My concern with laying the boards without fixing whilst putting the underfloor heating on is that they will bow and warp. I suppose I could maybe put weights on them.

The time delays is a bit of a problems as already I am advised I should wait six weeks before putting the underfloor heating on for the screed to dry.

Alex

 

[AMc]

I have to qualify that I haven't got a great deal of experience and I haven't done what you're proposing so I may have some of this wrong, but I've based what I've said on my understanding of wood movement from cabinet making TV and books.

The cracking noise happens at 7am when the heating kicks in after 9 hours of inactivity so it's the maximum temperature change. It's really loud and panicked me a lot the first couple of mornings.

The radiatior pipes have been pushed through holes barely bigger than the pipe - so I think they rub as the metal expands - metal will expand more then wood. I've tried filing them out but I'm not convinced I've done enough. The boards have been (re)laid with no more than 1mm between them which isn't enough to account for moisture expansion IMHO let alone heat. I've just discovered he used screws on one of the more warped boards which is now constantly under tension - trying to remove the screws to get a look I discovered he's stripped the threads. The other boards are full length and a foot wide so I'm scared of damaging them trying to lift them. I'm not sure what to do now but I suspect I'll leave them alone until we're sleeping in another room, then look at the problem again.

In my limited experience - if the wood is unevenly cut (i.e. not a straight section across the core of the original tree trunk) then it will warp as it warms up and it's moisture content changes. Looking at the ends of your boards if you can see the curve of the tree rings then the board is likely to cup in that way. As your boards have been in a building heated by fires their moisture content will be higher than a 'dry' central heated house. Add to that storing them outside in the cold and their moisture content will be much higher than when they are in your nicely warmed house. Screwing the boards to the joists in this state will create immense tension in the floor when the wood starts to dry out and change shape and might split 100 year old boards or at least create a very uneven floor.

In my opinion you are best to accept that some of the boards will warp a little and some a lot - if you can identify which are which before you finally arrange and fix them to the floor then you'll save yourself some pain.

 

[Alex F]

"Hi
You posted a thread about reusing your original pine boards over underfloor heating back in March.
We talked a bit but not much.

I'm seriously considering doing the same thing and I'd be very interested in your experience - either on the thread or via PM.
http://periodproperty.co.uk/forum/viewtopic.php?t=7653&highlight=floorboards+underfloor

Thanks

AMc"

Hi AMc

I did indeed use the floorboards with underfloor heating. I did as suggested as left them stacked in a heated room. By the time I laid the floor it was not longer cold enough to need the heating on so it was not until some 6 or so month that I properly tested the system. It has have not been a problem at all. I do not notice any gaps and no over expansion has occurred.

In the end we put battens over the screen and then the laid the floor boards. I'm not convinced the heating is as effective as it could be due to this but it maybe helping with floor board movement.

I think the boards are so well seasoned from their age that this helps. I also left a good deal of time after the screed was done before laying the boards.

Alex

 

[AMc]

I've been getting quotes for my renovation work - one of them is to replace the oil heating system entirely with an air source heat pump. I need to massively oversize radiators in the part already refurbed to deal with the low water temp.
As part of the quote we're doing a heat loss survey - I've discovered the floors in two rooms are old boards suspended over bare earth :shock: . There is a right gale under there

So now I'm looking at lifting them and insulating...then you factor in the cost of replacing the radiators with something victorian/reproduction and 2x oversized and suddenly it looks like underfloor might be a better bet (the rooms aren't that big to start with).

If I can do that without sacrificing my lovely Georgian boards then I may well go that way. Thanks for posting back.

 

[MdB]

As part of the quote we're doing a heat loss survey - I've discovered the floors in two rooms are old boards suspended over bare earth :shock: .

Earth under floor boards is common. Nothing wrong with that. It shouldn't touch the floor boards (or their wooden supports) though.

There is a right gale under there

Make sure that you don't stop the gale, its what is keeping your floor boards from rotting. A gale is good underneath the property though you may want to stop it coming up through your floorboards into your living room.

 

[AMc]

I know it's important to maintain ventilation to prevent the joists from rotting.

Considering the house was partially 'refurbished' in 1993 i.e. part of the house was fixed and the other half wasn't - I was a bit surprised that they didn't do anything to insulate the floors or stop the drafts in the main sitting room. Esp. as it looks like they sanded the floors and applied an 'oak' stain to the pine
In two other ground floor rooms they took up the boards, insulated and fitted new floors - odd, but I'm sure there was some logic to it somewhere.

 

[Matt Green]

I know it's important to maintain ventilation to prevent the joists from rotting.

No. It just reduces the risk of insect attack if your boards are sappy or are otherwise susceptible to it. Fungal spore germination requires a timber moisture content of 28% ish. That means that at 20C your subfloor would need to reach about 96% relative humidity. Not massively likely.

You might get a bit of furniture beetle damage and weevils nibbling the edges though.


Matt

 

[dandrew]

If the floor boards contain moisture, which they will, then the underfloor heating will dry them out, but you already know this. Seasoning them by leaving them in the room with the heating on will help reduce the moisture, but this is a slow process, and as you say, they may cup or twist. Putting them in stick, stacked on top of each other with small fillets of softwood between them may help, but the real test will be when they are in place on the joists.

Alternatively you can just accept that they will shrink over time, but use a method of fixing that will allow this to happen without splitting of the boards. The old timers used a method called slot screwing when they wanted wood to move without splitting. Screws were driven into (in your case) the joist so that the heads all stuck up by the same amount (usually 1/4" or 6mm). The heads of the screws were blackened and the boards place in position. Thus the mark of the screw head was transferred to the underside of the board. A hole slightly larger than the screw head was then bored and then a slot the same width as the screw shank and about 10mm long was made. The board was fitted over the screw head and then whacked with a mallet so as to drive the slot over the screw head. In this was the board could expand or contract without ripping itself apart, which it would if nailed down. Slot screwing floor boards would be a very labour intesnive job, and you would need a couple of mates to help with the mallet work

 

[Moo]

That doesn't sound like something to be attempted on an upstairs floor.

 

[Alex F]

So now I'm looking at lifting them and insulating...then you factor in the cost of replacing the radiators with something victorian/reproduction and 2x oversized and suddenly it looks like underfloor might be a better bet (the rooms aren't that big to start with).

Underfloor heating is well suited to my house as it has very thick walls and no cavity. I leave the underfloor heating on throughout winter. This suits the house as it takes about 2-3 days to properly heat my house up. I have conventional radiator in the bedrooms upstairs which work off a separate timer, and thermostat. I am very happy with this system.

If you lifting the floor boards and insulating the extra cost of UF heating may not be significant so it sounds quite likely to be worthwhile rather than the high running costs of oversized rads.

I have had no problems reusing my floorboards with the UF heating but it was a risk I took.