Green Building Forum - Venting a uninsulated wooden floor when all external walls are insulated ? Tue, 19 Dec 2023 07:07:45 +0000 http://www.greenbuildingforum.co.uk/newforum/ Lussumo Vanilla 1.0.3 Venting a uninsulated wooden floor when all external walls are insulated ? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17913&Focus=302685#Comment_302685 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17913&Focus=302685#Comment_302685 Tue, 01 Aug 2023 13:47:24 +0100 jamesingram I know we've been over this one a few times.
Tell me again why I can't block up the vents to a cold uninsulated suspended wooden floor when I've dropped EWI and cavity wall insulation down below dpc.
I know I'm not suppose to due to condensation, but if I don't the ventilation will just undermine the rest of the insulation.
It's nice a dry under there. If its made airtight , would it really be a major issue? :smile:]]> Venting a uninsulated wooden floor when all external walls are insulated ? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17913&Focus=302688#Comment_302688 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17913&Focus=302688#Comment_302688 Tue, 01 Aug 2023 17:48:42 +0100 djh
As long as there's a void, regs require ventilation, IIRC.]]> Venting a uninsulated wooden floor when all external walls are insulated ? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17913&Focus=302691#Comment_302691 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17913&Focus=302691#Comment_302691 Tue, 01 Aug 2023 19:39:30 +0100 tony Venting a uninsulated wooden floor when all external walls are insulated ? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17913&Focus=302694#Comment_302694 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17913&Focus=302694#Comment_302694 Tue, 01 Aug 2023 22:17:27 +0100 WillInAberdeen
'Cold' will be conducted under the foundations and into the soil below the floor. The EWI can not block this, unless it extends many feet below the ground. The cold will draw moisture vapour down from the house to condense in the soil (this is good).

If the condensation is not able to ventilate or drain away to somewhere safe, then the air under the floor will get cold and damp and rot the joists (this is bad).

Vents in old houses are small and get blocked easily, they have no oversite and dry soil is exposed under the floor, so the moisture can quickly soak away and sometimes this is ok, sometimes not.

So underfloor ventilation just gives some certainty that the moisture has a reliable route to escape, no guessing and easy to inspect.

The cold bridge from the foundations/underfloor always seems (to me) a disadvantage of EWI, and the equivalent bridge from the roof space down through gable walls. IWI can block these, but can have cold bridges in other places. Maybe a combo would work?]]>