Rotten Floor Joists

travel_freak

Hello,

After serveral months worrying what might be wrong with my floor ... it dipped in the corner along the outside wall ... I've now lifted the floorboards to have a look below.

The joists sit on the brickwork inside the external wall and at least three of them are rotten on the ends and one is very close to falling off the brickwork. As a result a couple of them have also twisted slightly.

They also smell badly of damp/rot.

My builder has suggested putting pads of concrete beneath, jacking up the joists and putting bricks etc., underneath to prop them up.

Please can anyone comment on the effectiveness of this?

Also is there any chemical I can paint or spray onto the joists to stop them from rotting further?

Many thanks.

Regards,

savemoney

I would have thought jacking the joists up and putting bricks underneath is a short term fix, my last house had this because previous owners cut corners

When wood starts to rot it needs treatment only proping it up will give you some extra time.

I believe you can treat the wood and wood can be strengthen with chemical but not sure if this works for joists

Fred56

You have to deal with the underlying cause. It's usually insufficient ventilation to the void beneath the floor. Typically an extension will be added to a house and the ventilation bricks will be lost down one side. The air can't flow through and over a period the humidity levels lead to fungal growth.

There will be rot and fungal spread on both the joists and the substructure brickwork. Propping up the joist ends may be a short term fix but it really needs tackling. Depends on your objectives and, if you're planning to sell, you ethics too.

Your builder will know all this. Cut out all the affected timber, burn it or get it off site. Scorch all the brickwork and have it treated with a fungicide (nasty stuff so watch your liabilities), treat any timber to be retained and ensure any new timber is teated timber of right structural grade and section to suit the span and loading - the builder will have a set of the TRADA tables. If he hasn't, ask building control - they are usually good people. Deal with the ventilation and check also the oversite surface at the bottom of the void- is there a lot of moisture rising from it, any organic material or growth? Modern standards would have the following over the subsoil - layer of sand blinding, damp proof membrane and say 50mm of concrete to limit ground moisture rising. There would be a minimum ventilation gap of 150mm between the concrete and bottom of the joists.

Well, you did ask.

travel_freak

Hi,

Many thanks for the replies.

To answer some of the questions:

There is no extension. The length of external wall is about 4 metres and there is one air brick. Block paving has been added outside but the level dropped by the air brick so that air can still get in. When standing inside and looking at the air brick under the floor daylight is visible so I assume air is circulating. It's a Victorian house so I guess they must have built it with just one air brick?

Under the joists is a drop down to what looks like bare earth with some sand - about 10cm/15cm I think. I doubt there is any damp proof membrane, certainly none is visible.

I've just spent a lot of money sorting out a damp quarry tiled kitchen floor so it would be difficult to have to spend more now having joists replaced which I'm sure will be expensive. (Does anyone know costs - or just to replace the rotten ends if this is possible?)

When people say this is a short term fix - how long would it be likely to hold up for? There is one joist at the far end which is already propped like this presumably by the last people who owned the house. That part of the floor is completely solid and seems okay.

What are the risks if I just do this?

How could I find out how structural these joists are - it is a ground floor room in a terraced house - the floor picks up all the noise and vibrations when my neighbours next door walk on their floor and when I mentioned this to a builder I had round he said I could cut away the joists completely and put a concrete floor in instead. But how do I know if that would be okay to do? I've always thought of joists as being major structural bits of a house and if I take mine away won't it affect my neighbours, it being terraced?

I'm beginning to wish I bought a new house now!

Many thanks.

27col

I have already posted this elsewhere. It might be of some interest.
Your symptoms sound suspiciously like dry rot. I had the same sort of rot in my first house and had to remove the floor completely and lay a new one. You can quite often tell if a floor joist has dry rot by feeling underneath it. If the bottom of the joist is concave(hollow) this is indicative of dry rot in the joist. If it is, then replacing the ends will be useless, as it the rot will re-infect any new timber. I hope it is not dry rot, because if it is, then it is a much bigger problem than you think. I suggest that you Google "dry rot" and see. There is a lot of information out there. It seems to spread by spores and the walls need to be treated as well. I remember that we burned ours with a blow torch to kill all the spores. As I have already said, I hope that you have not got dry rot, but make sure that you establish what sort it is, before wasting money on ineffectual treatments for the wrong problem. An extra air brick as far as possible from the existing would will help with air flow. Removing floor joists will not affect the house next door because they only sit in the hole in the wall. They will just maybe butt against next doors joists.