Advice needed on condensation in loft - old slate roof with no under felting
Anonymous user 16/03/2024 - 2.40 PM
Had a survey done on my 3 bed 1930's semi, which has an original, well-maintained slate roof, no under felting/membrane and it says:
"Significant staining is noted to roof timbers consistent with condensation. Staining of this nature is probably due to the recent installation of insulation material which has been installed right into the eaves, blocking a through flow of ventilation to the area. Action: Install vent tiles to front and rear roof slopes and pull back insulation to the roof eaves within the loft void to create ventilation within the area."
The insulation was installed some years ago under a govt discount scheme - guess it's not safe to assume that the guys who installed it knew how to do it properly! Also wonder if the surveyor was actually able to SEE that ventilation was blocked at the eaves, from his position on the loft ladder with his head through the hatch?
1. Is this a common problem? Roofers I've spoken to so far are reluctant to pull the insulation back, saying it's not something they do. Any advice?
2. Would you advise fitting vent tiles to this kind of roof and if so, what type?
3. Is it really necessary to move the insulation AND fit vent tiles?
(One roofer told me over the phone that he has never, ever put vents in a slate roof that didn't have felt underneath it..)
This is holding up my house move but I'm not sure what to do for the best. Thanks in advance.
Are you a tradesperson and able to answer this question?
you should be getting air flow from under the slates if there is no under felt if the insulation is pushed right into the eaves touching the slates it should be soaking wet and yes its really common mostly done on goverment advice run in a tv campaing a few years ago, you can usually tell just by putting your head up the loft if there is air flow,
roofs leak and always will that is the reason for under felt traditionally line mortar was used to catch any drips stopping dampness, there is a good chance you have nail fatigue which will be allowing water ingress into the timbers and the surveyour is taking this as a sign of condensation without looking its really not possible to be 100% sure of what is happening,
good luck alex
Hi Alex , while I agree with the previous comment , and given the age of the roof if you calculate to have the roof redone with a breather membrane etc that is your best scenario to move on with the sale . Pulling the insulation away from the eaves will help in the immediate action and should help drying out . Hope this helps
well the reply made was fairly correct. Normally there should be enough ventilation on a roof with no felt but additional vents at the bottom and top of roof will help.
The main reason as explained by other builder was the roof insulation being pushed too tight at the eaves and blocking any air flow. Air flow is the most important thing in the loft space. It gets rid of any damp air which can cause problems. I have dealt with this kind of problem before and pulling back insulation worked a treat.
Pulling back the insulation will help the air flow, the white stains is efflorescence (salt deposits) caused by moisture in the air and condensing on the nails, and if you look at the nails and they have rusted away then this will cause slates on the roof to slip out at this point it would be cost effective to replace the roof, if the roof doesn’t have nail fatigue then insert vents along the eaves on each elevation and only on one elevation at the top, do not put them on the top on all elevations, this is a mistake some roofers do.
Hope this helps
Regards Brian
