Underfloor insulation: will I get damp problems??

[KieraOwl]

I live in a 1920s semi. I am currently doing up the knock-through lounge/dining room, and it seemed like a decent time to think about putting in some underfloor insulation. (I am a southerner but live in the north, so am in need of some extra layers to protect my soft self from the harsh Arctic winds of Sheffield)...

My house is on a hill (where isn't, in Sheffield?) so the dining room has quite a large space underneath, while the lounge towards the front has less space. Was thinking of doing Kingspan board (or a cheaper equivalent) between the joists without any kind of membrane. Is this right?

However, when I moved into the house, the survey said that there was a bit of damp (minor, nothing serious) under the floor in the hallway. A company came in and said this was due to poor ventilation, so they put in a load of airbricks. I now have 6 (two on each side).

Will this be enough ventilation to insulate under the floor, or will I end up with a dripping, cold damp space and rot everywhere?

Advice v much appreciated!

 

[foxhole]

Underfloor insulation will be of little use more likely to cause damp problem, heat rises so unless you have a solid floor no point.

 

[JohnD]

underfloor insulation will not cause damp problems. Neither will a carpet or vinyl flooring. It will make a slight improvement to heat loss, which will be especially noticable if you have bare floorboards. You can use mineral wool quilt between the joists, which is easier to stuff into irregular gaps so will be better for stopping draughts round the edges of the room.i

However the underfloor space must be well ventilated with air bricks, whether you have insulation or not, otherwise the water vapour arising from the naturally damp soil under the house will not be able to escape.

 

[jabuzzard]

Underfloor insulation will be of little use more likely to cause damp problem, heat rises so unless you have a solid floor no point.

This is complete rubbish. Heat does not rise. I am frankly sick of seeing this utter nonsense being put out there by people who clearly have no clue how thermodynamics work.

Hot gasses are less dense that cold ones so they tend to rise. However and this is VERY important convection aka hot gases rising is one and only one method by which heat is moved about. The other two conduction and radiation make no distinction on orientation. Get a metal bar heat hold it vertically and heat the middle with a blow torch. You will find that the metal bar gets equally hot both above and below where the blow torch hits it.

In short insulating the floor WILL reduce the heat loss from a room which is why building regulations require all floors to be insulated these days.

 

[MissTinyMuscles]

Insulating the floor WILL make a difference. I presume that the air bricks you've installed are below the joists and therefore any insulation between the joists won't block them and cause a problem. I would recommend opting for an Earthwool roll or similar product because it is breathable (and much cheaper than the boards). I've done this recently underneath my Edwardian terrace and it seems to work well. If you end up using board insulation like Kingspan or Celotex you should fix it with battens right against the underside of the floorboards, leaving part of the joists exposed to the ventilation void.[/u]

 

[jagillham]

We've done exactly the same with kingspan between the joists, sure I read on the Energy Trust website 10% of heat loss is through the floor a while back.

Can't really comment on exactly what difference it made as we went from just floorboard and laminate, to kingspan, underlay and thick carpet... along with more loft insulation etc at same time.