Insulating Tin Roof

[Steebi87]

Hello,

 

We have just recently moved into a new home and there is a largest shed-like structure we are going to convert into a bar.

 

I am wondered what is the best way to insulate this kind of roof to stop condensation forming and dripping over everything?

 

thanks in advance to any replies.

 

[tonyshouse]

Insulated ceiling ventilation above - will be difficult 

[Ferdinand]

I did something similar but I need a bit more information.

 

How far apart and how deep are those joists and what is the angle of fall on the roof?

 

And is the roof completely waterproof?

 

And is it standalone or lean to?

Edited September 14, 2020 by Ferdinand

[Iceverge]

A quick look at the structure suggests you're not going to achieve any substantial level of insulation without great effort. 

 

To stop the drips,  a thin layer of closed cell spray foam,

Or 

just tack a roofing membrane under the joists supported with battens or something like chicken mesh to catch the drips. 

[Ferdinand]

..

Edited September 14, 2020 by Ferdinand

[Ferdinand]

This is the simplest version of what I did. You need to consider the depth you have and that you are happy with the strength of the front and back beams.

 

1 - Leave a generous ventilation gap below the tin - 75mm-100mm

2 - Drill 50mm holes into the ventilation space between each pair of joists through the beam at both ends. Insert 50mm soffit vents to keep insects out.

3 - Insulate using rolls of rockwool staple gunned between the joists. Can be pulled apart horizontally if needed.

4 - Electrical wiring as required for lights etc just on the side of the joists.

5 - Clad across the joists using whatever you want to use. You need to think about fire risk if any and perhaps a cladding with a vapour barrier depending on your assessment of humidity. 9mm ply and gloss paint might be suitable. 

 

I made it more sophisticated with a vapour barrier above the cladding to keep humid air from below out of the insulation, and a 50mm ventilation space by having a further soffit stood-off 25mm which allowed 25mm ventilation holes and a separated insect mesh on the vertical slot. I used 100mm of rockwool.

Critique welcome, but mine is still intact some years later.

 

Ferdinand

 

Edited September 14, 2020 by Ferdinand

[nod]

You could counter batton the underside with MF top hat Then fix insulated plasterboard 

It would leave good airflow and stop the drips 

[tonyshouse]

That wouldn’t stop the drips, they would land on the MDF which would swell and go mouldy 

[scottishjohn]

7 hours ago, Iceverge said:

To stop the drips,  a thin layer of closed cell spray foam,

yes would be my chouce 

the question is how much insulation in rest of this structure 

unless you going to insulate walls  and everything  and you  heat it to normal room temp you are going to make yourself a problem  .

whats the floor ?  concrete does it have DPC 

[joe90]

With my metal garage roof I simply laid a membrane under the metal roofing, it was to stop drips on my tools etc, works perfectly but For you it means lifting the roofing sheets. Any insulation can be installed underneath then.

[gc100]

28 minutes ago, joe90 said:

With my metal garage roof I simply laid a membrane under the metal roofing, it was to stop drips on my tools etc, works perfectly but For you it means lifting the roofing sheets. Any insulation can be installed underneath then.

This would be my vote as well. Ideally you want some airflow under the tin to dry it out. Something like tin over batterns with vented area at gutter level that goes up to vented cap in roof ridge. Then roofing felt on marine ply on your roof joists, then insulation In between roof joists. This would be similar to how you do a zinc roof on a house

Edited September 15, 2020 by gc100

[scottishjohn]

1 hour ago, joe90 said:

With my metal garage roof I simply laid a membrane under the metal roofing, it was to stop drips on my tools etc, works perfectly but For you it means lifting the roofing sheets. Any insulation can be installed underneath then.

seems a god solution --if you don,t mind striping roof 

might be simpler and cheaper to a get a frothpak and spray with closed cell foam  and get some imnsulation at same time --it will stop all condensation 

[Steebi87]

Hello, Thanks for all the replies. Ill try to answer as many questions as i can.

 

22 hours ago, Ferdinand said:

I did something similar but I need a bit more information.

 

How far apart and how deep are those joists and what is the angle of fall on the roof?

 

And is the roof completely waterproof?

 

And is it standalone or lean to?

 

The joists are 8" in depth and stand around 4ft between each other. Not reallly too sure on the fall of the roof (25degrees at a guess) and its a lean to from the main house.

 

20 hours ago, Ferdinand said:

This is the simplest version of what I did. You need to consider the depth you have and that you are happy with the strength of the front and back beams.

 

1 - Leave a generous ventilation gap below the tin - 75mm-100mm

2 - Drill 50mm holes into the ventilation space between each pair of joists through the beam at both ends. Insert 50mm soffit vents to keep insects out.

3 - Insulate using rolls of rockwool staple gunned between the joists. Can be pulled apart horizontally if needed.

4 - Electrical wiring as required for lights etc just on the side of the joists.

5 - Clad across the joists using whatever you want to use. You need to think about fire risk if any and perhaps a cladding with a vapour barrier depending on your assessment of humidity. 9mm ply and gloss paint might be suitable. 

 

I made it more sophisticated with a vapour barrier above the cladding to keep humid air from below out of the insulation, and a 50mm ventilation space by having a further soffit stood-off 25mm which allowed 25mm ventilation holes and a separated insect mesh on the vertical slot. I used 100mm of rockwool.

Critique welcome, but mine is still intact some years later.

 

Ferdinand

 

 

Are the gaps left by the roofing shape not enough for ventilation?

 

13 hours ago, scottishjohn said:

yes would be my chouce 

the question is how much insulation in rest of this structure 

unless you going to insulate walls  and everything  and you  heat it to normal room temp you are going to make yourself a problem  .

whats the floor ?  concrete does it have DPC 

 

Wall on the house side and opposite side are insulated with 75mm insulation boards of some kind. Wooden doors on the front and glass doors on the rear. We just have block pavers on the floor with carpets laid on top.

[Ferdinand]

13 hours ago, Steebi87 said:

Hello, Thanks for all the replies. Ill try to answer as many questions as i can.

 

On 14/09/2020 at 22:51, Ferdinand said:

I did something similar but I need a bit more information.

 

How far apart and how deep are those joists and what is the angle of fall on the roof?

 

And is the roof completely waterproof?

 

And is it standalone or lean to?

 

The joists are 8" in depth and stand around 4ft between each other. Not reallly too sure on the fall of the roof (25degrees at a guess) and its a lean to from the main house.

 

On 15/09/2020 at 00:22, Ferdinand said:

This is the simplest version of what I did. You need to consider the depth you have and that you are happy with the strength of the front and back beams.

 

1 - Leave a generous ventilation gap below the tin - 75mm-100mm

2 - Drill 50mm holes into the ventilation space between each pair of joists through the beam at both ends. Insert 50mm soffit vents to keep insects out.

3 - Insulate using rolls of rockwool staple gunned between the joists. Can be pulled apart horizontally if needed.

4 - Electrical wiring as required for lights etc just on the side of the joists.

5 - Clad across the joists using whatever you want to use. You need to think about fire risk if any and perhaps a cladding with a vapour barrier depending on your assessment of humidity. 9mm ply and gloss paint might be suitable. 

 

I made it more sophisticated with a vapour barrier above the cladding to keep humid air from below out of the insulation, and a 50mm ventilation space by having a further soffit stood-off 25mm which allowed 25mm ventilation holes and a separated insect mesh on the vertical slot. I used 100mm of rockwool.

Critique welcome, but mine is still intact some years later.

 

Ferdinand

 

 

Are the gaps left by the roofing shape not enough for ventilation?

 

No I don't think they would be OK because then the flat half of your roof gets no ventilation and you could end up with condensation in your insulation or between your layers. It *could* be alright but better to be as safe as possible etc. Also depends on whether you roof ridges are parallel or orthogonal to the roof ridges.

 

With 8" depth that's not a risk I see you need to take.

 

My opinion is that I would perhaps work with say 100mm or rockwool or similar, stapled to be about 15mm up the side of the joist, which would give you a gap above of approx 80mm. Then you have space to allow ventilation above.

 

The other driver for a larger air gap as I suggested is that the smallest soffit vents I know are 50mm, and structural strength of the perimeter beam needs to be maintained sufficiently.  

 

Cladding over the bottom of the joists is far easier than between beams.

 

You have not mentioned that it is a leanto - mine is and my airflow along between joists was towards the wall. I resolved that by leaving a 50mm gap between the tin and the wall, then flashing over with a wider grade of Ubiflex left ventilated at the ends.

 

Depending on which way your joists (and ventilation) run you need to think about the roof / wall join and satisfy yourself that it will work.

 

F

 

 

 

 

 

 

Edited September 16, 2020 by Ferdinand

[Steebi87]

On 16/09/2020 at 10:55, Ferdinand said:

 

Also depends on whether you roof ridges are parallel or orthogonal to the roof ridges.

 

 

Im not quite sure what that means.

 

Yes, it is a leanto which fixes onto the house. Are you saying that i dont need any kind of waterproof membrane as such?

 

If i were to drill hole for 50mm vents, would i install them in the area above the rockwool? and how often would i need a vent per joist?

[Ferdinand]

2 hours ago, Steebi87 said:

 

Im not quite sure what that means.

 

Yes, it is a leanto which fixes onto the house. Are you saying that i dont need any kind of waterproof membrane as such?

 

If i were to drill hole for 50mm vents, would i install them in the area above the rockwool? and how often would i need a vent per joist?

 

Sorry slight typo. It should have read:

 

"Also depends on whether you roof ridges are parallel or orthogonal to the roof joists."

 

I'll aim to come back this evening with a drawn detail.

 

F