Improving ventilation under suspended ground floor

[Charlie_B]

In process of buying 1920's detached house.
Original part of house has suspended wooden ground floor, 20 year old extensions on south and east sides are solid floor, leaving 4 airbricks on North wall and 2 on west wall to provide ventillation under original floor.

Following full structural survey, Surveyor's advice is to make the rest of the ground floor solid as well as he doesn't see any other way of emoving rick of dryrot developing (and of course he can't rule it out being present and there's no easy access to allow inspection)- don't really want to do his on grounds on cost and disruption - and reckon that its overkill as well.

Current state of underfloor timbers cannot be inspected at present, but there is no real flex in the wood floor.

Should ventilation on two adjacent sides be sufficient - is there a risk of a large area with little or no movement?
If so - does anyone have ant experience of pumping air under the floor to maintain air movement - thought is to pump air into the South East corner, "positively pressurizing the underfloor area forcing air to exit via airbricks in North and West walls - or any better ideas?

thanks
Charlie

 

[dandrew]

Presumably if there's no problem evident why try and fix it ?

We recently had dry rot eradicated in our hall, which was caused by a leaking lead roof on the portico that trickled water down into the floor joists and set up dry rot when the leading was replaced. This was evident as bouncy floorboards not cured by screwing them down and cuboidal cracking of the skirting boards. The true dry rot fungus was found as soon as we lifted the floorboards. We had to have the the joists & floorboards stripped out, spraying with noxious chemicals and the plaster & skirtings replaced. Not a cheap job - £2K all in. There was no ventilation to this part of the floor and there never had been (no air bricks in the portico), so the original 1862 builder didn't think it was necessary, which is good enough for me.

Why go to the expense of doing something that might be needed in the future but only IF there is a problem. Leave well alone in my view and wait and see if anything happens.

 

[Matt Green]

Following full structural survey, Surveyor's advice is to make the rest of the ground floor solid as well as he doesn't see any other way of removing risk of dryrot developing (and of course he can't rule it out being present and there's no easy access to allow inspection)- don't really want to do his on grounds on cost and disruption - and reckon that its overkill as well.

Arrrrrgh. *gnashes teeth*

He could rule it out by actually bothering to learn something about dry rot. Unless you have a source of fresh water (pipe, rainwater pipe) discharging under the floor or the building has a history of dry rot that was allowed to reach floor level and has been repaired and/or hidden above it, the risk is practically nil.

A lack of ventilation will not cause dry rot in sub-floor timbers. Insect attack, yes, if there is a lot of sapwood. Increasing the ventilation might lower the risk of insect damage, but unless you find out the structure of the floor it might be wasted effort.

Don't replace the floor, it's a waste of what is likely to be good quality timber. That the surveyor suggested it demonstrates he has a shocking lack of knowledge, competence and spinal rigidity.

Carefully lift a board or two at the edge of the floor where the joists bear into the wall. Find out what depth the sub-floor void is (who knows, a trap door might be possible) and how the joists are supported. Check the condition of the joist bearings, they might have wet rot decay if the ground levels are high.

If everything looks okay, put the boards back down and enjoy.


Matt Green