Sub Floor Ventilation

[tododo]

Hi all

Presently have a builder doing an extension on the back of house - the roof timbers have just started going in

Anyway - today decided to take the laminate up in the existing property we have had in for ~8 years - we have a damp / condensation issue in the timber floor!

There are a few beads of condensation visible on the underside of the floorboards in the problem area and there are a few rotten floorboards and probably a joist or two that will need to come out Gutted but at least we have found an issue I suppose - the house now smells of damp!

Anyway - the floor level outside the house is high ... and it was when we bought it - now that we have found an issue I have been googling and now realize we have no sub floor ventilation that I know of at all

We did have cavity vents on the outside but they were termed useless when we had cavity wall installation back when it was all the rage when we moved in - although we dont have any cavity wall damp yet - I still think it was a bad idea

So - the issue is we have no air bricks that I know of

Ive spoken to builder and hes said we could still put a couple of ducting vents in through the extension sub floor - he has laid the first layer of concrete base for the extension but still has to put insulation and a 50mm screed on top for underfloor heating

He said we could put ducting in but may have to cut out of the insulation - so thats an option I suppose but I was thinking that we could also duct air from the front of the 1930s bay window maybe??

As part of the process of building extension we have had the drive party removed and have noticed that there appears to be a 2nd drive underneath so we are planning to lower the levels outside anyway so that will help

Im going to take up a few floorboards in the bay tommorrow to see if there some air bricks there that maybe blocked either by the drive outside or the insulation

Does it sound doable to vent from the bay to the back room do you think?

Sorry for long post!

 

[Notch7]

Is there a reason you cant put in telescopic around the house.

Im not convinced ducting vents through an extension would give you enough airflow. For airflow you really need vents in opposite sides of the house.

Maybe the cavity insulation has led to the floor issue.

 

[tododo]

Yeh the cavity insulation could be the cause - where theres a gap for air to come in the underfloor brickwork - that was full of insulation - it was dry but still

Yes Ive been looking at those telescopics - was going to possibly put two of them in the front room if there are no air bricks in the bay already and then possibly another two for the back room (ducting through the house for those two in the back) - the hall will also need looking at also as again I dont think there is any sub floor vents - only a cavity vent

So the hall will also need venting to allow cross floor ventilation too

 

[^woody^]

If you have an original timber floor, then you have air bricks somewhere and need to reinstate them. To be effective, underfloor ventilation needs to be through-ventilation with vents on opposite walls, plus in any alcoves.

Whoever drew the plans should have included underfloor ducting into the design.

 

[tododo]

Just had a look today - there are a few cavity vents in the front of house - 4 in total - all above the floor level - as with all the other properties in the street too

So it looks like they are the vents for the underfloor as theres a brick removed below these vents in the sub floor too allow circulation

I dont think the cavity wall insulation has helped at all!!

 

[tododo]

Hi again - right so been looking at other properties in the street and they all have air vents above internal floor level - 3 to the front of property and two at the side
I think the way it works is that in the sub floor .... the inner brick is removed to allow the air in the cavity to vent below - so im thinking of taking all the old vents that I have out and replacing them to increase air flow - thats a good idea I think - but then to stop any cavity wall insulation dropping and blocking the vent Im planning to use some sort of flexible ducting
Is something like this a good idea https://www.wickes.co.uk/Manrose-PVC-White-Rectangular-Flexible-Ducting---100mm-x-3m/p/228677

Thanks again