Condensation problem in roof? Mystery!!

[MimiJane]

Hi,

I'm hoping someone out there can throw some light on a roof problem. We had the roof insulated in our 3 bedroomed detached 3 years ago, as well as cavity wall insulation. The roof insulation now amounts to about 14" of lagging. It's a small loft which you cannot stand up in. After about a year (in the winter), my husband had reason to go up into the loft and the lagging was wet through ... so bad we thought we had a burst pipe. We got the insulation people back ... no burst pipes, but they recommended we have vent tiles put in the roof due to the bad condensation, which we had done and they were properly fitted.

I noticed about a week ago that one side of our bedroom ceiling (exterior wall) had water droplets collecting about the coving and, on removing the water with a cloth, it was pretty wet.

My husband went into the loft and it was very damp along the perimeter of 2 sides of the house. A guy from the insulation company came out today and had a look in the roof and was baffled. He said it seemed well ventilated, there are no blockages between the eaves and the vent tiles are fitted correctly. He also checked the walls, etc. for leakages and could find nothing.

It's a complete mystery why we seem to have this condensation problem when we've done everything we can think of to prevent a build up.

At the moment, I have the heating on and all the windows ajar to try and keep it at bay! We really don't want to spend a fortune on getting roofers out if they can't determine what the cause is.

If anyone can offer any advice at all on what the problem is I'd be so grateful.

Mimi

 

[masona]

May need more ventilation, what type of soffit ventilation is it? Is it circular vent, if so, how far apart are they or are they continuous soffit vent? How many ridge tile vent do you have?

 

[MimiJane]

Just asked hubby ... we don't have soffit ventilation. We have two ridge (breathing) tiles and 6 venting tiles. The guy from the insulation company said that we should have done more than enough to stop condensation ... but we obviously haven't! No neighbours with similar rooves to us have got this problem as far as we know.

Thanks.

 

[masona]

We have two ridge (breathing) tiles and 6 venting tiles.

If you have roofing felt, can you see the felt is cut out around the vent tiles? If not, that's where the problem is. Normally the vent tiles are only ventilation under the tiles above the roofing felt. You really need air circulation from the bottom of the roof to the top.

 

[datarebal]

Make sure felt is cut allowing vent spigot into loft space, Get some short pieces of batten or off cuts of plastic pipe and slip these between the felt laps there by holding them slightly apart increaseing ventilation into your loft space. Fit as many as possible at all levels and full length of loft, then see if the problem stops, if it does then you know venting is the problem..
cheap easy and a simple DIY..
The additional air flow comes from normal tile blow by and can even work on a non torched slate roof.

 

[big-all]

the fact you keep looking wont help if you have bad ventilation as every time you open the trap door you introduce warm moist air

if you have the origional wood on the eaves make shure you dont have any insulation blocking the eaves to allow additional air flow

if you have replacement plastic then you will mayby have to as said above introduce some vents to improve circulation


is your trapdoor a good fit !!!!!!
if it lets warm air by it could agravate the problem
another possible source is gaps between the pipes into the attic needing filled as there will be no insulation under the tank causing a route for moisture that can condence on the bottom of the cold tank or add to the general dampness


how far up the roof are your 6 roof vents!!!!

 

[JohnD]

do you generate excessive moisture inside the house by draping wet washing on radiators or using the bath and shower without running an extractor fan? Do you use an unvented Condensor tumble drier?

Have you made any steam-vents into the loft by cutting holes in the ceiling e.g. for downlighters?

The vented tiles will let air out of the loft, but will not let fresh air in, so the air current will tend tro draw moist air up from the house. Eaves ventilatin will help a lot. It is also possible to make a hole in the end wall of the loft, if you have one.

 

[getmeoutofhere]

My Dad had a similar problem with loft condensation on a relatively new house. He cured it by putting a couple of air bricks into the walls at each end of the house.

 

[joe-90]

The vented tiles will let air out of the loft, but will not let fresh air in, so the air current will tend tro draw moist air up from the house. Eaves ventilatin will help a lot. It is also possible to make a hole in the end wall of the loft, if you have one.

I agree with what John is saying, it's actually the same principle that causes lift in an aircraft wing. The air going the long way over the roof will cause a partial vacuum in the loft. If there is no ventilation it will draw moist air from the house to fill the void.

 

[datarebal]

or from vents fitted on the opposite side of the roof