Condensation on rooflights

[Steevo]

Noticed today some water spots on the shed floor that are directly under the Z-purlin in the middle of the run of perspex rooflights. Rest of roof if FC sheets, but roof windows are clear perspex.

Is there anything that can be done to prevent/address this? I can see it being a problem otherwise...!

Having built my two grainstores without windows in the roof, just the ends, I've never come across this before but I certainly would never build a grainstore with rooflights like this shed. Asking for trouble.

 

[blackieman83]

Have fitted a second sheet on top of the original before to combat this problem using strips of butyl rubber tape as a kind of spacer to create an air gap of sorts between the sheets.

Maybe someone else will be able to say if this is a good idea or not, but it certainly worked on the few that I have done this way.

 

[Guss109]

Be interesting to find out how others deal with this as noticed the same yesterday

 

[Steevo]

@RWG Contracts will have a cunning plan I'm sure...!

 

[RWG Contracts]

No im clueless sorry. One problem with roof lights is you get condensation

 

[Tinman Steels Ltd]

We have supplied a customer with a big six outer sheet and insulated panel style box tray for the underside so it made it a FAIRs triple skin sheet. This was deigned to retro fit between the existing purlins. I know I have still got some sheets in the yard that are double skin I'm just not sure what the dimensions are but I'm sure there the same as the attached.

 

[Archie]

Think you are right about never building one with roof lights in the first place @Steevo
Noticed this problem on mine while the build was still ongoing and got them to replace with normal sheets before they left and glad I did. That was just single roof lights so imagine a run of them will be even more of a problem.

 

[Steevo]

Thanks guys. Not a very handy situation I'm in then - a storage guy moves in on Monday, and if we get another frost like that I know what my first trouble will be...!

I'll get onto the guys who built the shed and ask their advice.

Unfortunately, building control insisted on 10% roof lights, so now 10% of my roof drips!

@Tinman Steels Ltd - how does your system work please? Are you leaving the upper side of the roof as it is, and then fitting a "box" underneath with an extra roof light to trap some warm air?

 

[David.]

I've said it before, but the problem is much worse with 10ft clears than 5fts.
The condensation off a 5 ft disperses under the lap fairly easily because there is not much of it.
A 10ft requires a foam filler through the middle above the purlin, and this makes a break point where the water drips from. Hence the worst of the wet patch on the floor is under the middle purlin, and the condensation off the bottom half of the 10 ft sheet wicks away better, effectively like a 5ft.
I can fairly easily remove some the foam fillers in one of our sheds, and in the spirit of community research, I will try it.
The shed going up imminently will have 5 ft lights.

 

[Steevo]

I've said it before, but the problem is much worse with 10ft clears than 5fts.
The condensation off a 5 ft disperses under the lap fairly easily because there is not much of it.
A 10ft requires a foam filler through the middle above the purlin, and this makes a break point where the water drips from. Hence the worst of the wet patch on the floor is under the middle purlin, and the condensation off the bottom half of the 10 ft sheet wicks away better, effectively like a 5ft.
I can fairly easily remove some the foam fillers in one of our sheds, and in the spirit of community research, I will try it.
The shed going up imminently will have 5 ft lights.

You've got it in one! It's directly under the purlin, and I can see based on your explanation precisely why.

 

[Tinman Steels Ltd]

You would have to take out the current sheeting and fit the new ones with the box tray as the sheet is a whole unit. I will take a picture of one we have in the yard on Monday so you can see how it looks.

With your current sheeting having a central purlin as long as we had dimensions you can have the trays so you would have a box tray at the bottom between the purlins, then single skin over the purlin and again a box tray between the second set of purlins.

We have supplied these for customers that have had the Big 6 spray foam but this can be a bit harder to fit as you would have to cut some of the foam away.

 

[Tinman Steels Ltd]

Sorry for the delay @Steevo it's been a manic few days, i've attached a few different pictures of the top and bottom of the Big six fairs sheet. I hope this gives you more of an idea of how the sheets look.

 

[TripleSix]

Fit a length of guttering with end caps on under the affected purlins to catch the drips, they should hold enough to never need to be emptied as it will evaporate in warmer weather.

 

[Forever Fendt]

I've said it before, but the problem is much worse with 10ft clears than 5fts.
The condensation off a 5 ft disperses under the lap fairly easily because there is not much of it.
A 10ft requires a foam filler through the middle above the purlin, and this makes a break point where the water drips from. Hence the worst of the wet patch on the floor is under the middle purlin, and the condensation off the bottom half of the 10 ft sheet wicks away better, effectively like a 5ft.
I can fairly easily remove some the foam fillers in one of our sheds, and in the spirit of community research, I will try it.
The shed going up imminently will have 5 ft lights.

Good point

 

[TJltd]

If the building is now 'signed off' take 9ft 6in filons out cut to 5ft and fit a 5ft cemtent fibre above. All the condensation on the 5ft will be picked up on the fibre sheet below as there are no central fillers