Underfloor Insulation - Risk of Damp?

[grazza80]

Hi all, i've read quite a few different threads on installing installation under the floor, particularly around ensuring there is adequate air-flow to avoid damp. We're in the process of ripping out our current flooring, and as the house (circa 1900 build) is very cold in winter, we're looking at options to improve installation.

The concern we have is right now is whether installing insulation and sealing the floorboards / skirting etc. may creating a risk of damp on the joists. We're nervous the sealing / insulation itself will reduce any air-flow that was occuring from the living areas, and as the basement ceiling is flush with the joists there is limited opportunity for air to move under the joists. From inspection, we have only 1 air-brick (rear of property) and nothing on the front (or it has been rendered over).

No visible damp issues on joists currently, but would the installation of insulation and sealing significantly increase risk of damp? If so any thought on best option (e.g. installing further air-bricks - would this even help given the basement celining is flush with the joists?). Unsure how to protect against the risk of damp (with any degree of confidence) to avoid having to pull the floors up all over again!

Thanks Much!

 

[JohnD]

subfloors are not ventilated through the floorboards, they are ventilated through the airbricks. Clean out your from cobwebs and dirt. A subfloor void should be cool and draughty. If you are working under the floor, clear up any rubbish, especially organic material and scrap wood that can harbour rot. You should be able to see any blocked airbricks once you have the floor up. Mineral wool is good for blocking draughts as you can stuff it into the edges and corners. Get the brands with Ecose treatment as they do not shed dust and fibres.

If you have a basement then the ground floor should not be damp anyway.

 

[grazza80]

subfloors are not ventilated through the floorboards, they are ventilated through the airbricks. Clean out your from cobwebs and dirt. A subfloor void should be cool and draughty. If you are working under the floor, clear up any rubbish, especially organic material and scrap wood that can harbour rot. You should be able to see any blocked airbricks once you have the floor up. Mineral wool is good for blocking draughts as you can stuff it into the edges and corners. Get the brands with Ecose treatment as they do not shed dust and fibres.

If you have a basement then the ground floor should not be damp anyway.

Thanks John, I may have been off the mark thinking that given there is literally only one air-brick in the whole property, perhaps the sub-floor was not getting damp.

So potentially adding some insulation may not be a worry from a damp perspective? I was primarily worried warmth from living areas, would hit cooler air around joists (cooler air coming from the external air-bricks) which could create codensation.

Perhaps i'm jumping at shadows?

Appreciate the recommendation on mineral wool, i'd been reading the pro's and con's of various materials and that was what i was leaning towards!

Thanks again

 

[JohnD]

warm air, and water vapour, both rise upward, so are unlikely to travel into a floor anyway.