Roof vent tiles - how many and where to fit

[neutron]

I've had condensation in the well insulated loft of my house each year since buying it new 12 years ago. This year it was very severe and resulted in extensive mould/mildew. The problem was investigated twice by NHBC surveyors during the 10 year guarantee period and on each occasion their written report stated the roof space ventilation complied with requirements and condensation was normal during cold periods.
A further very recent inspection by a local builder revealed defective construction of the roof has caused rafter ventilator trays to be crushed and completely sealed between the top of the brickwork and the plywood panel supporting the leading edge of the tiles, i.e. there is no gap to allow air flow into the roof space. About 80% of the ventilators on the South facing front of the building are affected in this way and approximately 20% on the North facing side. The condensation is predominantly on the the North side of the roof when it occurs.
I've now been advised the only solution is to fit roof vent tiles on the South facing side, but I need advice regarding how many and where they should be fitted - low down the roof to attempt to achieve the originally intended crossflow or high level to allow the rising warmer air to escape.
Any help will be greatly appreciated.

 

[shirazman]

You need to vent the eaves and near the ridge and on both sides. Check out either Glidevale or Uubink sites where they should give you the proper spec for your size of roof. Hope this helps

 

[neutron]

You need to vent the eaves and near the ridge and on both sides. Check out either Glidevale or Uubink sites where they should give you the proper spec for your size of roof. Hope this helps

Thanks for your reply and advice, it sounds as thought this maybe an expensive problem to fix.

I have been told there should a sag in the sarking overlaps which would add to the airflow, in my case the overlaps are tight and it's been suggested that an inserts should installed at a number of joints but only on the front of the building as the ventilators at the rear are clear. Despite the fact the property is 12 years old and the NHBC guarantee has expired they are "considering" the matter and the builder has offered to install three roof ventilator tiles which does not seem adequate on a total roof area of approximately 114 sq.m.

Again thanks for your valued comments

 

[lorreal]

Hi,
The exact configuration can be found from the professional. You had better consult the one and find the estimate. From the practical point of view, tile roofing is very easy to install, maintain and modify. It does not take a lot to cut the tile and fit it to the right size. Installing the tile on the house is not very difficult. It is just a question of placing the tile and nailing it to the roof properly. Maintaining the tile is not difficult because you can simply remove the problematic tile and get it replaced by a brand new one.