Replacement Garage Roof

Sew_Late

I’ve got a prefab garage (the type made of panels that slot into grooves in posts and are then bolted together). At the moment it has an asbestos roof, which I’m looking to replace.

Most of the quotes I’ve had so far are for a flat roof with a timber structure, finished with felt. However, one roofing company advised me that a timber/felt construction might be too heavy for a prefab garage. They suggested that over time the extra weight could cause the walls to bow, and recommended a lined metal roof instead, which would be much lighter.  He's shown me pictures of metal roofs and it is quite an attractive look. 

This is the first time I’ve heard that weight might be a problem—none of the other companies raised it. All companies are well recommended. 

So I’d really appreciate any advice:

• Has anyone here had experience replacing a prefab garage roof?

• Has anyone used a metal roof, and if so what do you think of it?

• Is the concern about the weight of a timber/felt roof on a prefab structure valid?

Any thoughts or recommendations would be really helpful.

badmemory

Does your roof have concrete supports going across.  Besides the front & back mine has 3 with one that is where the roof panels overlap.  Just recently some of the concrete has broken off that middle panel exposing the steel? inside.  I am quite worried about it & will be reading along.

Swipe

I'd be inclined to go with the metal roof and can see it outlasting a flat timber and felt roof

https://www.jjroofingsupplies.co.uk/blog/how-long-does-metal-roofing-last/

WIAWSNB

I'd second the box section metal roof as it should be a direct replacement for the asbestos, is light, looks better, and it should easily outlast a felt jobbie. 
And, because it's a much simpler job, it'll likely be cheaper too.
Tbh, I wouldn't expect a ply/felt roof to cause weight issues, unless your garage was actually failing! But, metal is better.
Some folk find condensation forming on the underside, but this shouldn't really happen in a normal garage which tends to be naturally 'ventilated'! I understand you can get 'coated' undersides to help, and hopefully others will comment.
Have you had quotes?

Sew_Late

badmemory said:

Does your roof have concrete supports going across.  Besides the front & back mine has 3 with one that is where the roof panels overlap.  Just recently some of the concrete has broken off that middle panel exposing the steel? inside.  I am quite worried about it & will be reading along.

No it doesn't.  

Sew_Late

WIAWSNB said:

I'd second the box section metal roof as it should be a direct replacement for the asbestos, is light, looks better, and it should easily outlast a felt jobbie. 
And, because it's a much simpler job, it'll likely be cheaper too.
Tbh, I wouldn't expect a ply/felt roof to cause weight issues, unless your garage was actually failing! But, metal is better.
Some folk find condensation forming on the underside, but this shouldn't really happen in a normal garage which tends to be naturally 'ventilated'! I understand you can get 'coated' undersides to help, and hopefully others will comment.
Have you had quotes?

Yes, have decided to go with the metal roof. 

Anthony147

Sew_Late said:

WIAWSNB said:

I'd second the box section metal roof as it should be a direct replacement for the asbestos, is light, looks better, and it should easily outlast a felt jobbie. 
And, because it's a much simpler job, it'll likely be cheaper too.
Tbh, I wouldn't expect a ply/felt roof to cause weight issues, unless your garage was actually failing! But, metal is better.
Some folk find condensation forming on the underside, but this shouldn't really happen in a normal garage which tends to be naturally 'ventilated'! I understand you can get 'coated' undersides to help, and hopefully others will comment.
Have you had quotes?

Yes, have decided to go with the metal roof. 

@Sew_Late
Did you get this done, what prices / timescales are you getting quoted (what size of garage is it for - single / double)?

Sew_Late

Anthony147 said:

Sew_Late said:

WIAWSNB said:

I'd second the box section metal roof as it should be a direct replacement for the asbestos, is light, looks better, and it should easily outlast a felt jobbie. 
And, because it's a much simpler job, it'll likely be cheaper too.
Tbh, I wouldn't expect a ply/felt roof to cause weight issues, unless your garage was actually failing! But, metal is better.
Some folk find condensation forming on the underside, but this shouldn't really happen in a normal garage which tends to be naturally 'ventilated'! I understand you can get 'coated' undersides to help, and hopefully others will comment.
Have you had quotes?

Yes, have decided to go with the metal roof. 

@Sew_Late
Did you get this done, what prices / timescales are you getting quoted (what size of garage is it for - single / double)?

1 1/2 length garage.  Being done 1st October approx £3300 metal roof.  £4,300 for felt. 

Bigphil1474

We have a half sized concrete garage structure in our back garden and it has a fairly new metal roof - since we put the chest freezer in there we had a lot of condensation problems which caused the electrics to keep tripping. We've ended up with outdoor sockets and an outdoor light fitting inside.  

Section62

Bigphil1474 said:

We have a half sized concrete garage structure in our back garden and it has a fairly new metal roof - since we put the chest freezer in there we had a lot of condensation problems which caused the electrics to keep tripping. We've ended up with outdoor sockets and an outdoor light fitting inside.  

Condensation issues are almost a given with metal roofing in the UK climate.  The only way to be sure of stopping it is to have enough insulation in contact with the underside of the metal. Ventilation isn't enough on it's own.

Second-best is having anti-condensation fabric bonded to the underside of the metal - that doesn't stop the condensation, but it helps stop water dripping onto the contents of the building.

In your case the chest freezer has probably raised the temperature inside the garage by enough so the temperature differential between the inside and outside of the metal is good for condensation forming.

WIAWSNB

Sew_Late still has time to arrange that 'insulated' option.

Having said that, I think I have mentioned before on this forum a large open 'car port' outbuilding in a farm we walk past regularly, fully open along its front, and corrugated steel roofing. A few cars always parked under it, and washing machines and driers along the back - never ever have we seen the inside be other than bone dry, regardless of the weather. 

But, that would require complete ventilation. Better to add that insulating layer, like the fabric-bonded type, from the off.