Condensation forming on inside of garage roof

[KyleT]

I have a condensation problem on the inside of my garage roof. I noticed it in November, lots of condensation forming on the roof but only at the back half of the garage which is slowly being converted into a utility room. This hasn’t been a problem before, my only thought was maybe the tumble dryer was causing the problem as it is also located in the same area. I decided to buy some foam insulation at 75mm thickness as the void between the wooden beams and the garage roof was roughly 150mm therefore I knew using 75mm would leave another 75mm air gap between the insulation and roof. I did the job using foil tape to seal all joints and even spray foam in small gaps but make everything as air tight as possible.

Today I decided to check the roof, running along side the garage is a full length passage way that has the same flat roof as the garage and I didn’t insulate this part as I wanted to inspect the garage roof over the utility room for more condensation. To my horror it is probably worse now. Water drops are dropping onto the foil back foam insulation with more condensation forming on the roof. It’s also so cold in there at the moment that some of the water is turning to ice. I can only assume one of two things is the reason.
1.) I need to also insulate the passage way too or

2.) some how the tumble dryer is still managing to penetrate through the insulation and create condensation. I’m slightly at a loss here. I’m not a great DIYer but will do what I can to sort this issue if anyone has any ideas?

 

pictures can be seen here - https://imgur.com/a/IakHvYU

[epsilonGreedy]

Where does the exhaust air from the tumbler go, direct outside via a hole or into the internal airspace of the garage?

[Jason L]

The air gap above the insulation needs to be ventilated to the outside air, i guess its not.  and your need a mechanical extract in there the tumble drier / utility room area.

Edited January 7, 2021 by Jason L

[Temp]

Guidance on this subject here..

https://www.tendringdc.gov.uk/sites/default/files/documents/planning/building control/Flat roof guide.pdf

 

If you insulate between the rafters you are making what if called a "cold roof" design. This simply means that the structural components of the roof are on the cold side of the insulation. If water vapour can get to this area it may condense on the now colder roof members.

 

In summary you need to do the following (and do it well)..

 

1) Form a void above the insulation and adequately ventilate it to the outside as per the guide..

2) Add a vapour barrier below the insulation.

 

It sounds like you have been doing this but perhaps not well enough?

 

In particular the amount of ventilation is important. Ideally you want vents on two opposite sides at the eaves to encourage a cross flow. 

 

 

[KyleT]

43 minutes ago, epsilonGreedy said:

Where does the exhaust air from the tumbler go, direct outside via a hole or into the internal airspace of the garage?

It’s a condensing tumble dryer so it just creates heat in the room

[KyleT]

43 minutes ago, Jason L said:

The air gap above the insulation needs to be ventilated to the outside air, i guess its not.  and your need a mechanical extract in there the tumble drier / utility room area.

I’ve just come across these https://www.roofingsuperstore.co.uk/product/klober-flavent-upvc-roof-breather-vent-standard-flange-100mm.html?gclid=CjwKCAiA_9r_BRBZEiwAHZ_v1wM_HjOK-Kn-w5AB_ULoYdv7Ic4FHr77_Ndq_R2Z4Rd6BXjx0trN2BoCp4oQAvD_BwE hopefully they can be fitted to the existing epdm. 

[KyleT]

40 minutes ago, Temp said:

Guidance on this subject here..

https://www.tendringdc.gov.uk/sites/default/files/documents/planning/building control/Flat roof guide.pdf

 

If you insulate between the rafters you are making what if called a "cold roof" design. This simply means that the structural components of the roof are on the cold side of the insulation. If water vapour can get to this area it may condense on the now colder roof members.

 

In summary you need to do the following (and do it well)..

 

1) Form a void above the insulation and adequately ventilate it to the outside as per the guide..

2) Add a vapour barrier below the insulation.

 

It sounds like you have been doing this but perhaps not well enough?

 

In particular the amount of ventilation is important. Ideally you want vents on two opposite sides at the eaves to encourage a cross flow. 

 

 

There is a void of about 75mm above the insulation. There just doesn’t seem to be much ventilation. I’ve come across these https://www.roofingsuperstore.co.uk/product/klober-flavent-upvc-roof-breather-vent-standard-flange-100mm.html?gclid=CjwKCAiA_9r_BRBZEiwAHZ_v1wM_HjOK-Kn-w5AB_ULoYdv7Ic4FHr77_Ndq_R2Z4Rd6BXjx0trN2BoCp4oQAvD_BwE hopefully they do the trick. I have fitted a vapour barrier. I’ve simply taped up all joints and edges of the insulation. 

[scottishjohn]

would vapour barrier not be better above the insulation --so if any condensation forms purely by temp dif it does not come through --

any slight gaps in insulation will allow hotter air to go up and start the condensation at the joints

many cases of this with sips panlled roofs in alaska  causing rot  of osb sheathing in the panels at the panel joints when using shingles on directly top  of panels -- solution was to make a second roof with a void  so they have a draught and shingles stay cold  .like you would do with a tiled roof using batons to lift them off and giving a gap 

Edited January 7, 2021 by scottishjohn

[Temp]

8 minutes ago, scottishjohn said:

would vapour barrier not be better above the insulation --so if any condensation forms purely by temp dif it does not come through --

any slight gaps in insulation will allow hotter air to go up and start the condensation at the joints

many cases of this with sips panlled roofs in alaska  causing rot  of osb sheathing in the panels at the panel joints

 

Not sure how you can easily put one above the insulation (on a conversion I mean).  

 

https://www.nicholsonsts.com/news/blog-dont-get-caught-out-ignoring-vapour-control-layer#:~:text=Be it a cold or,structure and causing interstitial condensation.

 

Edited January 7, 2021 by Temp

[Temp]

 

[scottishjohn]

pefect job for spray closed cell foam 

but I understand where he is now -and if like your picture he cannot get a draft though very easily to dry up any moisture - so could be just trapping in moisture to rot roof  above 

If this space is going to be heated that makes it worse 

[KyleT]

18 minutes ago, Temp said:

 

Not sure how you can easily put one above the insulation (on a conversion I mean).  

 

https://www.nicholsonsts.com/news/blog-dont-get-caught-out-ignoring-vapour-control-layer#:~:text=Be it a cold or,structure and causing interstitial condensation.

 

As per the picture above my thought would be to install some breather vents in the roof at least 2 vents between each joist (so maybe 6 to 8 vents) and hopefully that should solve the issue?

[Jason L]

Yes some mushroom vents like that will do a the job, it might need working out how many you need. 
If it’s open on that side bit you want to insulate that section as well, to close the gap above the insulation off from the room. 

[KyleT]

1 hour ago, Jason L said:

Yes some mushroom vents like that will do a the job, it might need working out how many you need. 
If it’s open on that side bit you want to insulate that section as well, to close the gap above the insulation off from the room. 

So I need to completely close the gap in the passage way like I have done in the utility too, and then fit the mushroom vents. This will be adequate ventilation? 

[Jason L]

4 minutes ago, KyleT said:

So I need to completely close the gap in the passage way like I have done in the utility too, and then fit the mushroom vents. This will be adequate ventilation? 

what i mean, is in the 3rd pic, where there isnt any insulation there is a gap above the wall, where the air can get above the insulation, if the insulation is the other side of the wall.  that wants to be closed off if this is the case.

[scottishjohn]

I would remove what you have done so far --let it dry out and get a froth pak -closed cell kit --job done - and if you want to then sheet the joists --no problem 

you can rfit your solid insulation after  if you like and get even better insulation

 I hope your tumble dryer has a direct connection to the out side world or you will be making another problem 

 the thought of making numerous holes in your roof membrane to vent the void is a bad idea and maybe making more areas that could leak 

 

https://www.abbuildingproducts.co.uk/froth-pak-600-spray-foam-kit.html

Edited January 7, 2021 by scottishjohn

[KyleT]

1 hour ago, scottishjohn said:

I would remove what you have done so far --let it dry out and get a froth pak -closed cell kit --job done - and if you want to then sheet the joists --no problem 

you can rfit your solid insulation after  if you like and get even better insulation

 I hope your tumble dryer has a direct connection to the out side world or you will be making another problem 

 the thought of making numerous holes in your roof membrane to vent the void is a bad idea and maybe making more areas that could leak 

 

https://www.abbuildingproducts.co.uk/froth-pak-600-spray-foam-kit.html

So, just so I understand, this stuff would fix my problem because it completely covers the internal side of the roof and is a much warmer surface than the wood is therefore preventing condensation if any humidity hits the foam?

[scottishjohn]

22 hours ago, KyleT said:

So, just so I understand, this stuff would fix my problem because it completely covers the internal side of the roof and is a much warmer surface than the wood is therefore preventing condensation if any humidity hits the foam?

and because it is stuck to the wood of the roof there is no cold surface anywhere on underside  so no  condensation