Ventilating New Ground Floor

[leedjc]

Hi all, and I hope that you had a merry Christmas!

We are shortly about to rip out all the old floor and subfloor in our early 1800s mid terrace.

We were originally going to go down the limcrete route, but budget is tight and we're not going to be able to afford it. Anyway, we've decided on a timber floor, got the structural requirements all sorted etc, so that's no problem. My main issue is how to deal with ventilating the floor void. The exterior ground level is the same as the finished floor level, so ventilation bricks can't be used, plus we can only use the front elevation of the house for ventilation as the back section of flooring will meet the concrete slab from the extension.

Any thoughts/ideas? How necessary is the ventilation? The new floor joists will be 150mm away from soil as per regs, so no real issues with those drawing moisture through capillary action

 

[freddiemercurystwin]

You can use telescopic vents to cope with the higher ground level. Venting the void is essential. If you cannot provide adequate ventilation then timber is an unsuitable choice.

 

[leedjc]

Thanks Freddy

After doing some quick fag packet maths, it seems that the savings on putting down a timber subfloor is fairly negligible, plus with a limecrete slab, we could put in a decent UFH system.

Ventilation at the front of the house isn't a big deal, it's trying to vent it any the back which is more of an issue!

 

[theprinceofdarkness]

Perhaps I have got it wrong, but I am thinking that your front wall is straight on to the pavement. With a cottage of this age it is unlikely to have a DPC or cavity walls. As your FFL is level with the pavement, how are you going to deal with water running along the pavement?
I considered a telescopic vent, it will need a lot of the front wall removing as the whole body of the vent would have to be hidden within the thickness of the wall, then I thought, what would happen if splashing water got inside the vent, it could turn your under floor void into a swimming pool, perhaps a bit unlikely.
Frank

 

[leedjc]

Yes you're right. Our house does face straight into the pavement. To make matters worse, we are at the bottom of a small valley, so the water table is quite high here.

Some water splashing is inevitable, but shouldn't be a big deal if you place the air brick high enough.

Our house is stone with no dpc or cavity. It's all possible, but I'm thinking that limecrete is going to be better in the longer term.

The current ground floor is currently 2/3 cement slab (causing damp issues in the internal walls), with the other third being suspended timber - with no ventilation I may add!