Roof sagging

[Swifty1234]

The roof has always sagged in our motorhome and I think it has had a previous repair from inside as the roof lining is slightly different. I've checked with a damp meter today and I'm getting over 40% damp around the roof window. I've checked other places and it's all around 13% so I'm confident it's confined to this area. I've run a straight edge over the width and it sags by about 2" in the centre but the perimeter seems straight and true. I did hose the roof down and use a soft broom last week but didn't put any weight on it. Any advice greatly appreciated

 

[Swifty1234]

 

[oldiesontour]

Interior roof panels off would be the first step in order to see how extensive the likely rot is.

 

[Swifty1234]

 

[Swifty1234]

It's worse than I feared, there are actually two places where it is coming in. By the skylight and to the far left where there coincides to be a small crack in the outer roof which again seems to have had some shoddy repair. I'm not getting damp readings anywhere else down low etc. It looks like the roof in this area is constructed with 2x2 and floor insulation which I'm guessing wasn't original?

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[Swifty1234]

 

[oldiesontour]

Can't tell by the photos ..but Is it that the original timber was shaped to give a slight rise to the outer skin and was replaced with off the shelf thereby leaving the outer skin unsupported in the centre? My first thoughts maybe get 3/4 marine ply and laminate 2 or 3 thicknesses shaped as required bond insulation to timber and outer skin ( having coated any damaged areas inside with a good Pu adhesive. as it will flex a little glass fibre being a bit rigid perhaps) another useful product may be plasterboard foam adhesive(soudal Screwfix) it holds 8x4 sheets of plasterboard to any backing permanently and Wooden skirting to walls etc..it's like expanding foam but doesn't expand as much you apply it wait a few minutes then fix

 

[Swifty1234]

Sounds plausible about the original timber being curved. By 3/4 do you mean 18mm ply? That would be heavy surely and I would think sag eventually anyway? Or do you mean 3 or 4 thin ply sheets and laminate those?

 

[oldiesontour]

No 19 mm (2thick bonded back to back to replace the existing 2 x 2

 

[oldiesontour]

Basically glue lam beam..easier to shape more stable and stronger than 2 x 2 softwood

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[Swifty1234]

I see what you mean. I don't suppose you can buy them pre made anywhere

 

[oldiesontour]

Would t of thought so it's going to be a one off profile.could also be done with aluminium or thin wall steel box with a wooden or metal profile added to carry the outer skin

 

[Swifty1234]

Apologies, it's not 2". It's more like 32mm. I'm guessing I would need a steel prop to lift the roof back into shape and then install the curved glue beam laminate or steel truss? Doesn't feel like I've got a lot of depth to play with.

 

[PP Bear]

Get it done and get rid is my advice.

 

[oldiesontour]

Maybe something like this profile could be a decent soft wood

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[oldiesontour]

Or could you screw a/bolt a piece of either angle or box alongside the existing timber to straighten and stiffen it then if the outer skin looks ok from outside use either adhesive or plasterboard foam to secure outer skin to timber and insulation then to refit ceiling..new faced ply sold by the likes of magnum motor homes

 

[kingoftheroad]

It's worse than I feared, there are actually two places where it is coming in. By the skylight and to the far left where there coincides to be a small crack in the outer roof which again seems to have had some shoddy repair. I'm not getting damp readings anywhere else down low etc. It looks like the roof in this area is constructed with 2x2 and floor insulation which I'm guessing wasn't original?

Hi Swifty1234
The slight roof sag, is probably down to the new timbers bowing slightly and is more a cosmetic issue than a structural one. However, the roof bowing in this area, is allowing rain water to flow and collect, directly around your skylight, hence the leak.
If you want to keep the work load and costs to a minimum and end up with same result:

Place a flat blade putty knife, between the skylight framework and the aluminium roof sheet, then very carefully prise apart the alloy sheeting from the frame, the staples, will probably, just pull through or break away. Then once cleaned up/fixings removed, you will have enough access to enable you to, slide thin flexible lengths of plywood between the vans roof sheet and it's framework. Pack the roof evenly to each side, but you also need a slight gradient, example, 3 packers around the skylight frame, down to 2 further out, then to, until the roof looks cosmetically improved, but more importantly, the skylight once bonded back in place, will be level, or ever so slightly elevated, to enable the water to naturally drain away from it.
Mike

 

[Raul]

I wouldn't use any wood truss/ beam. I would look for 40mm schletter solar rail and use that profile as a beam, each side of the window. Its strong, light and can fix any metal brackets with self drilling screws.
Alternatively ally square box profile, but the rail I suggested is cheaper and stronger.

 

[oldiesontour]

Hi Swifty1234
The slight roof sag, is probably down to the new timbers bowing slightly and is more a cosmetic issue than a structural one. However, the roof bowing in this area, is allowing rain water to flow and collect, directly around your skylight, hence the leak.
If you want to keep the work load and costs to a minimum and end up with same result:

Place a flat blade putty knife, between the skylight framework and the aluminium roof sheet, then very carefully prise apart the alloy sheeting from the frame, the staples, will probably, just pull through or break away. Then once cleaned up/fixings removed, you will have enough access to enable you to, slide thin flexible lengths of plywood between the vans roof sheet and it's framework. Pack the roof evenly to each side, but you also need a slight gradient, example, 3 packers around the skylight frame, down to 2 further out, then to, until the roof looks cosmetically improved, but more importantly, the skylight once bonded back in place, will be level, or ever so slightly elevated, to enable the water to naturally drain away from it.
Mike

What has caused the crack ..I guessed the sagging timber has either left the roof unsupported or it's bonded to the timber and been stressed as a result ?? Like to know your thoughts as you obviously have direct experience

 

[Swifty1234]

Many thanks for all the replies. Much appreciated. Having taken some more of the insulation away it looks like the crack is actually more of a cut. I suspect something has punctured the skin and torn it, it's about 100mm long from inside and has been poorly repaired. I think it will need repairing from inside and outside with some sort of patch or plate? I'm trying to understand all your suggestions and will hopefully draw them out on autocad so I fully understand.

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[oldiesontour]

I wouldn't use any wood truss/ beam. I would look for 40mm schletter solar rail and use that profile as a beam, each side of the window. Its strong, light and can fix any metal brackets with self drilling screws.
Alternatively ally square box profile, but the rail I suggested is cheaper and stronger.

I thought Ali box but for the age of the van steel box would outlast the van is more readily available cheaper and a thin wall box will work with self drilling and not weigh much more...the timber profile would put the outer skin back to the right shape and support it as well as giving an easy. fix for the inner skin

 

[kingoftheroad]

What has caused the crack ..I guessed the sagging timber has either left the roof unsupported or it's bonded to the timber and been stressed as a result ?? Like to know your thoughts as you obviously have direct experience

Hi
Can't say exactly, there doesn't appear to be a dent, if it was stress related i.e. the roof panel rattling in transit, i would expect stress around fixed areas, not randomly in an area shown.
Carefully cut away the styreen sheet in that area and view the actual split from the underside and take the job from there, this would also be the best approach to its repair (patching it from inside out)
Mike

 

[kingoftheroad]

Hi
Can't say exactly, there doesn't appear to be a dent, if it was stress related i.e. the roof panel rattling in transit, i would expect stress around fixed areas, not randomly in an area shown.
Carefully cut away the styreen sheet in that area and view the actual split from the underside and take the job from there, this would also be the best approach to its repair (patching it from inside out)
Mike

If you go down the replacement frame route, make a complete frame up and put back into place in one piece and also change the direction of the timberwork, so that the skylight supporting timbers go the shorter way, reducing the cross member length, which in turn will reduce the chance of bowing.

 

[Swifty1234]

Sorry it's a tear, not a crack. Must have hit something prior to my ownership.

At the moment I'm thinking a replacement frame is a must. I don't fully understand the other approach which I think is to remove the skylight and install thin strips of plywood between the insulation and aluminium outer skin? Perhaps I have that wrong. Probably need to read again.

The 40mm schletter solar rail sounds good, I wonder if I could bend it slightly to give a slight curve? Perhaps not needed. I know a good blacksmith who has a specialist bending press.

 

[oldiesontour]

Sorry it's a tear, not a crack. Must have hit something prior to my ownership.

At the moment I'm thinking a replacement frame is a must. I don't fully understand the other approach which I think is to remove the skylight and install thin strips of plywood between the insulation and aluminium outer skin? Perhaps I have that wrong. Probably need to read again.

The 40mm schletter solar rail sounds good, I wonder if I could bend it slightly to give a slight curve? Perhaps not needed. I know a good blacksmith who has a specialist bending press.

If you could bend box then the inner skin is contoured in both directions very difficult to clad....what ever you decide good luck for a satisfactory outcome!

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[kingoftheroad]

Sorry it's a tear, not a crack. Must have hit something prior to my ownership.

At the moment I'm thinking a replacement frame is a must. I don't fully understand the other approach which I think is to remove the skylight and install thin strips of plywood between the insulation and aluminium outer skin? Perhaps I have that wrong. Probably need to read again.

The 40mm schletter solar rail sounds good, I wonder if I could bend it slightly to give a slight curve? Perhaps not needed. I know a good blacksmith who has a specialist bending press.

Hi
If the timber framework is not rotten, or it's fixings have not come adrift, it's just bowed, you can strip it all out and replace it, or pack the area at which it's bowed, by placing diminishing plywood strips on the top of your existing framework, to correct/level out, the upper alloy skin.
If done correctly, it's not a bodge, just a lot cheaper/easier and achieving the same result.

 

[Swifty1234]

Current layout

 

[Swifty1234]

Possible layout with change of direction

 

[Swifty1234]

Perhaps a bit OTT?

 

[Swifty1234]

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