mould growth due to insulation ?

[Glenn Spray]

Hello All ,

last year I got the cavity walls insulated and topped up the loft insulation myself to save energy/ money etc ,but I now seem to have a problem that in all the upstairs rooms at the joint of the ceilings and the walls I am getting a lot of mould spores appearing this isprevalent on the outside walls only .

My question is should the loft insulation go right up to the point where the roof trusses meet the top of the walls or should I leave a gap and if so how big a gap ? .

Its a semi house by the way / and we didnt have this problem last winter

Thx in advance for any replies Glenn

[Mike]

Is there more condensation/damp in the hse that might indicate a blocked vent?

The stuff they use to insulate shouldn't wick water from the outside walls.

Mike

[Andrew Gabriel]

The point of leaving a gap is to avoid blocking the roof ventilation. How is your roof ventilated? You should be able to run the insulation right up to the walls, but you will probably have to reduce the tickness to keep at least an inch (and preferably two inch) gap under the felt or tile backs.

If you have a real problem getting convensional loft insulation over this area, you could get a sheet of 1" Cellotex and cut bits to fit over the last few inches where you can't get the loft insulation to fit. Glue it to the back of the plasterboard so air can't circulate under the Cellotex (which would defeat it).

I guess this is the one remaining cold spot, due to no insulation on top of it, so it's where condensation is going to form in the rooms. Infra-red thermometers are very good at identifying cold spots like this.

[Glenn Spray]

Hi Mike ,

There is only the normal sources of condensation ie shower/bath in the bathroom (I have a ceiling extractor fan but this doesnt appear to draw much moisture away !) and breath moisture in the bedrooms .

all the condensation spot appear on the walls with the windows below , this probably has something to do with it due to the cold air possibly ?

thanks for your reply

Glenn

[Glenn Spray]

Hi Andrew,

Theroof does not appear to be ventilated at any point itis tiled with black tar? felt underneath .Icannot see any vents at any point within the roof , does this mean the roof is vented where the trusses meet the top of walls ?

do you think i have blocked the ventilation ?

thks for your help

Glenn

[Mike]

If the damp spots are only above the windows it's likely that condensation is forming on the lintel above the window. As this year has been a very mild winter all over the UK and this didn't occur last year it suggests the hse has become damper this year.

As the shower extractor doesn't seem to be working v well it could be the insulation has blocked it, can you remove the grill and check the vent for blockages. Plse remember to switch the fan off at the mains first!

Mike