re roof problem

[wood master]

hi all i posted not so long ago about this problem here are some photos of the workshop

my question was what is the cheepest way to keep my workshop warm and dry eg: drip of the tin roof

thanks all hope you can help

 

[marcros]

you need to stop warm moist air getting up there and condensing, so I would personally probably go with some fibreglass loft insulation, and any means possible of securing it.

A quick google brings up http://www.wickes.co.uk/building-materi ... c=SP050365 at £5 a roll- may be good price, bad price, I haven't checked. Homebase were doing it cheap here, but I don't know how cheap.

Ideally, you would secure with some form of sheet material- ply, osb etc. You mention the cheapest solution though, so really anything would do that would keep it up there- even tile lathe if necessary would be better than you have now, although it wouldn't secure it greatly. (also the problems of bits falling down, loose fibres etc). Something like a landscaping fabric would probably do at a push- you have plenty of beams to secure it to.

 

[wood master]

what does anybody think of airtech foil insulation, will it keep the heat out in the summer and the heat from the fire in ?

 

[marcros]

i dont think so. I bought some some years ago, or something similar for a development that I was buying the materials for, and had a look at the specs and how it worked. I think that it works because there is next to no air movement within a cavity wall. It goes in the middle, and so is surrounded by a static air gap both sides, as well as being basically bubble wrap itself. At best, you are only going to get half the benefit, and I am not sure that you will get it airtight enough to get that. I may be wrong.

Thick bubble wrap itself may assist your situation, by making a false ceiling. Of course, the airtech would also do that, but would cost more.

 

[Mark A]

Sorry to jump in, but doesn't the fibreglass insulation get damp?

mark

 

[beech1948]

The roof as implemented will always be subject to warm air condensing on it so drips will always happen.

Possible solutions such as fiberglass insulation will help but will not stop warm air rising to hit the roof. If fiber glass is used it will prevent some of the damp but not all.

Most suitable solution is to get the roof sprayed with closed cell foam insulation to a depth of 3 to 4 inches. If this is too expensive or unpalatable then maybe consider replacing the metal roof with a metal pre insulated roof using the existing roof structure.

bearer of bad news
Al

 

[PMK54]

B&Q have subsidised glass fibre on offer at the moment. But I agree with the earlier 'spray foam' post, moisture would get through the fibre and the fibre would hold it next to the roof and encourage the growth of fungi etc. I guess a pro foam spraying company would advise on whether priming/undercoating the roof if is required.

 

[marcros]

would something like http://www.tecpaints.com/newsFull.php?id=34&start=0 help?

 

[Dibs-h]

Looking at the pictures - FG insulation could be put between the rafters and the metal roof, ensuring it is as close a fit to the metal skin.

Then cut and fit Kingspan or similar between the rafters. You could use FG or Rockwool batts here as well.

You need to seal the roof panels at the ridge and at the eaves first.

2 things - 1st is insulate and 2nd is to fit some kind of vapour barrier on the inner face of the insulation, i.e. room side. Now Kingspan already has that. If what you fit doesn't have it, then you need to fit it. Poly of a sufficient thickness can be used. OSB\Ply are deemed vapour impermeable (if of sufficient thickness). If you don't fit one - then you will have problems (potentially) with moisture making it's way thru into the insulation (assuming it's FG\Rockwool) and condensing.

HIH

Dibs

 

[lincs1963]

To insulate that roof you need to put kingspan or similar between the rafters but ensure that it is at least 25mm away from the roof sheeting.As it is only a workshop 50mm of kingspan would be fine. you must ensure that the insulation has no gaps in it so that warm air cannot get into your 25mm air space. DO NOT seal the roof at eaves and ridge as the airflow is required to prevent damp and mould. Up until a few years ago venting was catered for by soffit vents and/or ridge vents, nowadays there is no need as breathable membrane is used instead of roofing felt.
You can then skin over the interior with plasterboard, thin ply, hardboard or any sheet material really.
Hope this is of interest, regards, Neil

 

[Dibs-h]

To insulate that roof you need to put kingspan or similar between the rafters but ensure that it is at least 25mm away from the roof sheeting.As it is only a workshop 50mm of kingspan would be fine. you must ensure that the insulation has no gaps in it so that warm air cannot get into your 25mm air space. DO NOT seal the roof at eaves and ridge as the airflow is required to prevent damp and mould. Up until a few years ago venting was catered for by soffit vents and/or ridge vents, nowadays there is no need as breathable membrane is used instead of roofing felt.
You can then skin over the interior with plasterboard, thin ply, hardboard or any sheet material really.
Hope this is of interest, regards, Neil

Neil

Why do you say that the air gap should be left - i.e. vented roof?

The roof covering is impermeable and therefore no moisture should penetrate the metal roof. I've seen similar metal roofs in industrial units, having worked on them and the insulation is to the back of the metal roof, eaves and ridge are sealed.

In this case, I'm of the opinion that a breathable membrane or roofing felt is completely wasted due to the impermeability of the roof skin.

Vented roofs are common where the roof covering is traditionally tile\slate - never seen one on a metal skin roof. Look at the case where industrial units have metal roofs where 4" or so of PU foam is factory bonded to the back of it.

Dibs

 

[plug]

We are still venting roofs with breatherble felts at ridge and soffits. BC still require it and the arcitects are still drawing them on the plans.

 

[galwayworker]

Hi Dibs,

The reason for ventilating between the roof covering and the insulation doesn’t have anything to do with the actual roof covering. You are right in that no moisture will penetrate the metal roof but moisture can still occur on the underside of the metal roof when warm air condenses on its surface. When insulating the underside of roof say with a Kingspan board it’s very difficult to completely fill every gap fully. The warm air will find the gaps between the insulation boards and this warm air can then cause condensation. The ventilated air gap between the insulation and metal roof is to try and get rid of this condensation and dry out the insulation / roof members.

Looking at your photographs the ideal method would be to cut insulation boards to size and fit them between the rafters. You are right in that a breather membrane / roofing felt won’t be of any benefit here. I’m not sure how efficient a vapour barrier would be as it’s an old building and getting an airtight seal between the old walls and roof could be an issue.

In industrial roofs where the insulation is bonded to the underside of the metal there isn’t any gap between the insulation and metal so there isn’t any space for condensation to form.

Oh and I wish I had a workshop as big as yours…..

J.B.

 

[Dibs-h]

Hi JB

Cheers for the post. I see the reasoning. I think that with a little though and planning air leakage can be all but reduced. You could fit Kingspan between the rafter and then place 1" (min) Kingspan boards across the inner face of the rafters (I'd be tempted to use 2") staggering the joints. If you fitted a vapour barrier over the inner face of the rafters, after having put insulation in between the rafters, then the complete boards over the lot - it would get fairly airtight.

Foaming the gaps between the rafters\insulation and the whole sheets, should seriously reduce any air leakage.

Tyvek do a product called SD2 which I've used and the spec gives very good ideas on how to reduce air leakage.

Dibs.

p.s. Workshop - glad you like it. About to start the adjoining garage and it's basement. Not looking forward to that.

 

[lincs1963]

To insulate that roof you need to put kingspan or similar between the rafters but ensure that it is at least 25mm away from the roof sheeting.As it is only a workshop 50mm of kingspan would be fine. you must ensure that the insulation has no gaps in it so that warm air cannot get into your 25mm air space. DO NOT seal the roof at eaves and ridge as the airflow is required to prevent damp and mould. Up until a few years ago venting was catered for by soffit vents and/or ridge vents, nowadays there is no need as breathable membrane is used instead of roofing felt.
You can then skin over the interior with plasterboard, thin ply, hardboard or any sheet material really.
Hope this is of interest, regards, Neil

Neil

Why do you say that the air gap should be left - i.e. vented roof?

The roof covering is impermeable and therefore no moisture should penetrate the metal roof. I've seen similar metal roofs in industrial units, having worked on them and the insulation is to the back of the metal roof, eaves and ridge are sealed.

In this case, I'm of the opinion that a breathable membrane or roofing felt is completely wasted due to the impermeability of the roof skin.


Vented roofs are common where the roof covering is traditionally tile\slate - never seen one on a metal skin roof. Look at the case where industrial units have metal roofs where 4" or so of PU foam is factory bonded to the back of it.

Dibs

I can see what you are saying but when the insulation is bonded to the material there is no gap at all for air, however if you retrofit insulation to existing at the very least you will have air channels where the corrugations are. To make this part of the roof airtight would be almost impossible. it is better to hedge your bets and build in some airflow.
I am not suggesting that a membrane is needed in this case.
The foam type eaves fillers that are used on box profile roofs are air permeable so they alone will not create a seal.
One of my many jobs some time ago was erecting 300' x 80' poultry sheds, the roofs where sheeted on the inside first (underlined). they were then insulated withv quilted fibreglass. Different areas of the country had different reg's for insulation thickness so we had to fit different sized purlins to ensure that the quilting didn't come into contact with the outer skin and restrict the airflow.
Hope this has explained why I believe airflow should be maintained.

Best regards, Neil

 

[wood master]

thanks folks theres a lot to think about there, but the besy way to go i think is to put kingspan up and seal as bet i can.

thanks for all your input.