Re-roof ventilation

[Charlie6]

Hi, I am in the process of getting quotes to reroof a 1940's semi detached house with a hip roof and an unventilated cold roof design. The roof will be just be used for storage rather than a usage room.

Roofshield will be used as the membrane and a dry ridge hip and ridge system will be fitted. I have been in contact with the roofshield manufacturer and they have advised that no additional ventilation is required with the membrane.

I am concerned about condensation once the insulation (type as yet undecided) is installed between the loft floor joists and wanted to find out:

1. Do all dry ridge systems provide ventilation as standard?
2. Will additional cross ventilation been required?
3. Are tile vents worth having and is there any way to work out how many you require? My neighbour has one tile vent on each side of his roof about half way up (3 in total).

I would rather the ventilation issues are resolved whilst the roofing work is being carried so if I need to be thinking about something else please let me know! Thanks very much.

 

[Alastairreid]

Follow the manufacturers advice, what you have is perfectly adequate.

 

[freddiemercurystwin]

Personally, for the tiny cost of say three tile vents each side I would add them, there are occasionally issues with condensation even though a breathable membrane has been used.

 

[^woody^]

Recent investigation into modern air permeable roofing membranes has found that they are not performing as well as expected and lofts are experiencing condensation issues - even if installed and ventilated as per the manufacturers instructions.

Look for an "air-open and vapour-permeable membrane" product to BS 5250 2011.

Not all dry ridges provide specific open ventilation, but some are ventilated through the membrane (which is not cut), which can be sufficient. You need to get a specific dry ridge if you need additional (open) ventilation.

Tile vents are crap, and are not for use when re-roofing. If you need ventilation, fit it at the eaves and ridge

Edit: spelling

 

[noseall]

Recent investigation into modern air permeable roofing membranes has found that they are not performing as well as expected and lofts are experiencing condensation issues - even if installed and ventilated as per the manufacturers instructions.

Yeah, I've been saying the same thing.