U/floor heating with timber floorboards? To do or not to do?

[blissbaby]

We have just bought an old farmhouse in NE Scotland. We are planning to lift the original pitch pine floorboards and install a wet underfloor heating system, then re-lay the floorboards.

We have received lots of conflicting advice regarding this, and the latest is that we shouldn't install same, as all wooden floorboards have a moisture content, which will dry as the heating is on - causing the boards to contract. Then as the heating is off, the boards will expand again. Appratently if this is the case, this will cause movement which will in turn cause plastered walls to crack.

How likely is this? The floor boards are in excellent condition (having been protected by a series of wildly patterened nylon carpets over the years) and they are straight and thick, with little or no gaps. Moreover, the wood has been there possibly since the house was built, in 1895 - surely they would have seasoned by now?

What do you think? Is this a potential disaster? And if so, what do you recommend we do?

Thanks for any help.

BB

 

[simond]

It will depend primarily on the moisture content in the timber, you need to clarify this.

I have had a similar question from a customer in Surrey; I can't warrant his old pine floor won't shrink and warp. Chances are, it will when dried out by UFH.

 

[JohnD]

Will it be occupied or heated 365 days a year? if not, the floor will expand and contract every time the humidity changes.

If it is an old house the wood may be old, but will never have been as dry as it will get when you roast it from below. It will crack.

 

[Agile]

I would start by asking what you hope to achieve by a UFH installation.

If you have properly researched UFH then you will know that its best on 24/7. It also needs about 50-100mm of insulation under the floor!

On 24/7 I would expect that it will be fairly OK but remember the wood will lower the heat transmitted to the room which will need a higher temperature underneath the floor making the problem worse.

UFH is fine in a well insulated property. An old farm with solid walls and little insulation does not sound like an ideal situation for UFH unless you are adding 50-100mm of insulation to the walls.

Tony

 

[blissbaby]

Wow! Thanks for such speedy and helpful reponses!

We plan to have heating on 24/7. We are currently removing all lath and plaster walls and ceilings to put in insulation, then plastering again. The loft will be heavily insulated too.

We are putting in good level of insulation u/floor too - Kingspan is the product of choice, it seems.

How would we check the humidity of the wood? And what would be the cut-off point for UFH?

Thanks again -
BB

 

[Agile]

My Protimeter has a scale for moisture content of wood.

A cabinet maker might have some useful input and a posting or the woodworking part of the site might give more advice.

I would expect that it will be very difficult for you to predict the problems in advance. Age, type of wood, will all have an effect.

If I had to give advice it would probably be dont!

If you still went ahead then I would advise that you would have to be prepared to give up the wood floor and have ceramic tiles if the movement proved to great.

Wood should be left or loose laid for several weeks in the climactic conditions its to be used in before its permanently fixed.

Its easy to leave an expansion gap at the sides and ends so cracking plaster is not a problem.

Tony

 

[JohnD]

I suppose you could experiment by putting a piece of antique furniture on top of a radiator, and watching it warp and crack.

I have the feeling you don't like the advice you are getting so are planning to ignore it.

 

[Deluks]

I thought that water supplying ufh is at a lower temperature than that which feeds a rad?

Will the floorboards be exposed, possibly with small gaps in between that will let the heat rise up?

 

[DaveSmiler]

I have placed underfloor heating in my bathroom, using the central heating pipes that feed the radiator on a circuitous route under the floor boards.

Of course, all timber prior to use in construction is seasoned. However, there will often be at least some moisture in materials such as wood because moisture is generally all around in the environment. Having said that, all floor boards I've ever seen seem pretty dried-out to me - I don't think there can be much moisture in them where some form of heating has been in pace for a while and dampness avoided.

The fear you have is of the boards cracking because the source of heat is close. In any house that has hot water central heating there are hot pipes running under floorboards all over the place. How often has anyone found cracked floorboards over any of these pipes? I haven't!

Another fear is that the plaster might crack as a result of boards expanding and cracking. I don't see why this would happen. In all houses I've seen, plaster is not attached to floorboards. Floorboards are attached to joists which rest in the walls, while plaster is attached to walls and typically stops at the skirting board above the floor. Thus the woodwork and the plaster are typically not connected.

Perhaps you could treat the boards with a healthy dose of wood oil (both sides if you're lifting them up). This will help keep the boards looking good and be in good condition. It will provide appropriate "moisturising" but won't be easy to dry out because oil won't evaporate the way water moisture can.

Also, you could have your under-floor heating thermostatically controlled in order to constrain the amount of heat.

Many people have underfloor heating in their houses, don't they? I wouldn't worry too much about this. I'd get done what I want to see done.

 

[mointainwalker]

|and they are straight and thick,

How thick ? Since wood is quite a good insulator, this will (significantly ?) reduce the efficiency.

The usual way to moderate this problem is by using aluminium spreader-plates which fit around the pipes and are attached to the boards. This may be difficult in your situation.

 

[blissbaby]

Thanks for all your replies. We are now investigating another option which is to remove all the wooden floors totally and replace with a solid concrete floor. This would eliminate all the problems mentioned above but I would expect that it would be at great cost. Obviously we would insulate if we decided to go down this route. We are getting some estimates and wll post back when we have more information. Thanks again!

 

[beccablackdog]

I know this topic is old and I am new but I was just looking to see more about it because I have been debating with a friend about this situation. She wants to put underfloor heating in a barn she's converting but I am convinced it is a bad idea - mainly because I recently noticed how much the floor of a friend's converted oast has been affected by it.

They put theirs in about ten years ago and the boards have shrunk & cupped, with big gaps between. These were the original boards, so over 100 years old.

My friend says her builder is going to do a moisture test etc etc. and that underfloor heating is 'easier'... I noticed the comment of one poster here about putting an antique on a radiator and watching it shrink - and I think he/she is on the money! My sister bought an antique dresser here in England and exported it to the States and has now had to buy a humidifier because it can't cope with the dry atmosphere of the area she lives in.

When I went to investigate the idea of UF heating for a new extension to my house the flooring people insisted that the only wooden floor suitable would be engineered wood. In the end I opted for slate since it is such a good heat conductor.

 

[swedeman]

Yes and the post is getting older , but I have a little real life living with farm houses, underfloor heating and wood floors so hopefully this helps:

To completely remove an old fine pitch pine floor and relay will not be easy. It is likely the removal will damage the floor and it will not go back so well. I would be tempted to sand and wax the lovely floor as it is - this is something you can't buy!

From experience, in an old farm house or barn the moisture content of the floor is likely to be well over 10%, and when relayed onto a heated floor, the pine boards will shrink significantly with some doming and possibly cracking. And yes, the shrinkage can be alarming and even over normal heating pipes.

Wooden floors are one of the worst type of flooring materials to set over a heated floor, as they insulate rather well, most woods will move alot with the heating.

From Experience, well seasoned oak that had been allowed to acclimatise in situ for several months, sat well on a heated floor and was very confortable. Biggest problem was the insulative properties of the wood, giving a long time to heat up (so needs to be on 24 hours) and when cold, other sources of heat were needed.

 

[Mangobananas]

Hi, most interesting thread. Despite all the con's with this approach with the worst for my circumstances being poor heat conduction of floor finish, can anyone advise how they would go about fixing the boards to the concrete screed in respect to the floor finish - concrete piecing floor brads? Assuming the boards, antique pitch pine, will acclimitise without warping.

 

[blissbaby]

Forgot all about this post. Thought you might like an update.
We attempted the UFH under original floorboards. Didn't work. On many levels! We laid the pipes, etc etc, re-laid the floor (which was a backbreaking and lengthy job to do), and put the heating on in very very small increments of a very very long time - can't remember exact timings but it was a couple of months. The floorboards have cupped and gapped. Also, as suspected, not enough heat getting through.
So we are going down UFH-compatible radiator route. And the floorboards are going to be a nightmare to sand now
Thanks for everyone's suggestions and comments.
BB