ᐅ Unventilated Wooden Flat Roof – Waterproofing and Insulation?
Created on: 2 Jul 2013 09:56
C
chris.12Hello everyone,
I am planning to build a new flat roof for a bungalow built in 1964.
Due to various requirements, it will be constructed as an unventilated flat roof in a timber frame with insulation between the rafters.
I am aware of the challenges involved in this type of construction and do not want to start a discussion about the pros and cons; my question concerns a specific detail.
From the inside to the outside, the construction will be as follows:
- Gypsum board ceiling
- Installation level / counter battens
- Intelligent vapor retarder
- Support layer with insulation between rafters (24cm (9.5 inches))
- Roof sheathing OSB
- Roofing membrane, black PVC (no green roof, no gravel)
The roof will have a slope of 2-3%, created by wedges placed between the roof beams and the roof sheathing.
So far so good, now for the question:
Because of an eaves overhang on one side of the building, the insulation between the wedges that form the slope will be “open” to the adjacent box for the external blinds. While it won’t be exposed to rain, there is effectively a form of ventilation on this side that narrows toward the middle of the roof following the slope. This ventilation obviously will not function properly because it is neither continuous nor tall enough.
Now I wonder whether it might be harmful to have this opening to the insulation (a pseudo ventilation) at that spot, or not. Would it be better to close the openings between the wedges?
I hope my description is reasonably clear.
Thank you very much and best regards from Hagen
Christian
I am planning to build a new flat roof for a bungalow built in 1964.
Due to various requirements, it will be constructed as an unventilated flat roof in a timber frame with insulation between the rafters.
I am aware of the challenges involved in this type of construction and do not want to start a discussion about the pros and cons; my question concerns a specific detail.
From the inside to the outside, the construction will be as follows:
- Gypsum board ceiling
- Installation level / counter battens
- Intelligent vapor retarder
- Support layer with insulation between rafters (24cm (9.5 inches))
- Roof sheathing OSB
- Roofing membrane, black PVC (no green roof, no gravel)
The roof will have a slope of 2-3%, created by wedges placed between the roof beams and the roof sheathing.
So far so good, now for the question:
Because of an eaves overhang on one side of the building, the insulation between the wedges that form the slope will be “open” to the adjacent box for the external blinds. While it won’t be exposed to rain, there is effectively a form of ventilation on this side that narrows toward the middle of the roof following the slope. This ventilation obviously will not function properly because it is neither continuous nor tall enough.
Now I wonder whether it might be harmful to have this opening to the insulation (a pseudo ventilation) at that spot, or not. Would it be better to close the openings between the wedges?
I hope my description is reasonably clear.
Thank you very much and best regards from Hagen
Christian
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