Ventilation - poly-carb covered lean-to with UPVC door

[reubin78]

I (think I am) looking for advice about ventilation!

We have recently (2 weeks ago) replaced an old glass lean-to roof with a poly-carb equivalent. We have also replaced the UPVC door.

We have already noticed a significant amount of condensation on the underside of the poly-carb roof. My assumption is that this is a consequence of the new roof being an air-tighter fit and there being no ventilation?

Does this seem logical? Do I need to add an air brick or two? Both ends of passageway? High or low?

Useful facts.....

The lean-to spans the kitchen wall (with wooden back door and single glazed sash window) and a double brick garden wall.

The approx footprint is 4.5m long x 1.2m wide

The intended use is as a porch so somewhere to keep coats, shoes - hence don't want it to be a damp space.

 

[Harry Bloomfield]

The intended use is as a porch so somewhere to keep coats, shoes - hence don't want it to be a damp space.

It is an uninsulated cold space and so will always suffer high levels of moisture. You could improve it by increasing the ventilation, but it will always be a problem. Does it get better if the door is left open a little? You could try adding a vent at either end to improve it a bit.

 

[reubin78]

The wall (left of photo) is essentially a double brick external wall. I have considered insulating the wall (the upvc door is offset for that very reason) but have held as I wanted to see how the space behaved before hand. Ironically, my concern was that insulating it may make it too warm and result in condensation!!

I have been working in the passageway tonight - grouting a small area of tiles. Internal and external doors shut. When I was cleaning up I noticed the roof was wet underneath so I have wiped off the excess water and opened the external door - that bit of air made a difference. (I must remember to go and close it!!).

This suggests some sort of vent would help - but how many and where. I don't want to create a cold space with a draft blowing through it - just a sufficient amount of air circulation.

 

[Harry Bloomfield]

The wall (left of photo) is essentially a double brick external wall. I have considered insulating the wall (the upvc door is offset for that very reason) but have held as I wanted to see how the space behaved before hand. Ironically, my concern was that insulating it may make it too warm and result in condensation!!

I have been working in the passageway tonight - grouting a small area of tiles. Internal and external doors shut. When I was cleaning up I noticed the roof was wet underneath so I have wiped off the excess water and opened the external door - that bit of air made a difference. (I must remember to go and close it!!).

This suggests some sort of vent would help - but how many and where. I don't want to create a cold space with a draft blowing through it - just a sufficient amount of air circulation.

A through flow, end to end ventilation is always more effective.

 

[reubin78]

Vents located at top or bottom?

 

[reubin78]

I was just thinking/reading about trickle vents as they seem typically small/compact.

"If you are not sure about the size of your existing vents, remember that all habitable rooms (bedrooms, living rooms etc) should have a minimum of 5000mm2 of free area ventilation and all wet rooms (Bathrooms, W/C etc) should have a minimum of 2500mm2 of free area ventilation. To give you an idea, one trickle vent usually provides 4000 sq mm of ventilation."

Seems to suggest that we shouldn't need too big a size of vent. Any suggestions anyone?

 

[RandomGrinch]

Hi,

As it doesn't seem to be the most critical of spaces to keep dry, you can afford to take a slightly experimental approach!

Adding a trickle vent to the uPVC door is an easy DIY job, though it does involve chain drilling into your new door!

You can get kits for a few pounds:
https://www.amazon.co.uk/Merriway-BH05603-Windows-Adjustable-Trickle/dp/B074PXY9VK

Although, some dislike them for the draughts they can create and for getting filled up with insects/debris.

It would also be better to have some cross ventilation as Harry suggested; something in the wall at the other end would be beneficial.
You can get devices such as 'anti draught' or 'black hole' ventilators that can provide passive ventilation without allowing a howling wind to pass through!

If this doesn't work, you can always add some more ventilation, even perhaps an extractor fan. Though again, as Harry says, it is very unlikely that you will remove all the condensation issues. There is a law of diminishing returns!

 

[reubin78]

Thanks guys.

I've read a few similar posts (to mine) and it seems that simple things like draught proofing/sealing the door from the kitchen would help (stop warm air getting into passage).

I'll google those ventilators too.

 

[Harry Bloomfield]

I've read a few similar posts (to mine) and it seems that simple things like draught proofing/sealing the door from the kitchen would help (stop warm air getting into passage).

Yes, the warm moist air from cooking in the kitchen will make it much worse.

 

[Mr Chibs]

Insulation won’t stop the condensation either, you still have dampness coming up through the floor.

Ventilate as mentioned.

I’ve just built a Lean to canopy, and get no condensation, but it’s open on two sides, so the wind takes all the moisture away.