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Old 05-26-2015, 05:40 PM   #1
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Cold flat roof - no space for ventilation...?

Hey guys,

I'm doing renovations to my old 1905 house in the Netherlands, and I'm running into issues with our flat roof.

Basically, our roof has a terrace above. The roof already has flat windows installed, so we cannot have a warm roof as the extra height would be too much.

Previously, there was plasterboard inside on the ceiling, but *no* insulation. So I guess condensation was not an issue. Plus it was not a 'livable' roof, so it was done on the cheap - I guess.

So I went with the idea of having a cold roof. My problem is that I simply cannot have ventilation. The joists run adjacent with the house. At the front side, we have the house (multiple stories) - so we can't put a vent. We also can't do a wall vent because there are big double doors going out to the terrace.

At the other end, at the end of the house, is the neighbours house. This time it is also only 1 story, so we have the option of having some kind of vent on top of the roof - but is that an option? I've only seen vents on the wall, between the joists.

Is it possible to do this another way? Perhaps having some kind of device that circulates air? Or perhaps vents on the top of the flat roof? And if so, can I somehow have a single vent instead of multiple vents between the joists (that would be a total of 14...

Any help would be appreciated. I'm stuck.

I've attached some pictures. They are, in order:

- facing the front of the roof, where the rest of our house is
- the back wall. Neighbours house behind this wall.
- same as above
- view of the roof from above, looking towards the neighbours.
Attached Thumbnails
Cold flat roof - no space for ventilation...?-img_2190-1-.jpg   Cold flat roof - no space for ventilation...?-img_2189-1-.jpg   Cold flat roof - no space for ventilation...?-img_2188-1-.jpg   Cold flat roof - no space for ventilation...?-img_2183.jpg  
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Old 05-26-2015, 06:52 PM   #2
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Is the roof being re-done?

You could strap the roof and create a new vent space above but if not, the easiest thing is probably SPF in this case.
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Old 05-26-2015, 08:43 PM   #3
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Welcome to the forum!

Another option is R-15 rigid foam board (XPS or EPS w. vapor barrier) insulation tight to roof decking and canned foam the joints/perimeter. That would give you 43% Relative Humidity in the house before condensation (board sheathing at 44*F), same as Zone 4a (see map) here;

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