shed Upgrades wood heater & bitumen black

[Rattrap]

Hi all,
After too many cold cold winters in the shed where temps can reach a balmy 4c at midday i finally bought myself a wood heater. Its a 44 gallon drum on its side with a professional door kit fitted into what was the base. I've placed it well away from anything that makes sawdust & my dust extractor will soon go into a small shed outside. I've had it fired up once so far & it really puts out the heat well & can take some good size pieces of wood.
Now to the next job today; painting all the steel C-section rafters with a brush on bitumen. Thru the winter i have a really bad problem with condensation on the rafters. Whenever we get a frost thru the night condensation gathers on the rafters then freezes. When the sun comes up it thaws & i get a mini rain in the shed - all over my cast iron machinery & any projects i happen to be working on. This only happens when we have a frost but never when it rains so i'm pretty sure its not a leak in the roof. Up to now i've had to cover everything with tarps, which works but is a pain in the butt plus there's always something that gets missed with a tarp that somehow is also under a rafter.
Pics 2 & 3 shows the water stains left from many years of water droplets. Lets just hope that the pain on bitumen will do the job!

[RufflyRustic]

Love the couch next to the firebox:2tsup::D. With 4 degrees C at midday:o, brrrrrrrrrrrrrrrrrr. I agree - mini-rain inside the shed is Not fun!

Why did you choose the brush on bitumen? I've never heard of that before.

[Rattrap]

RR i chose the paint on bitumen mostly because of recommendations from several people. The black stuff is specifically designed to go onto steel so theres no need to prime the surface or anything else. Also Tar doesn't freeze to therefore - hopefully - neither will any moisture on the rafters.

[RufflyRustic]

Ah Ha! Thanks Rattrap. I will be very interested to see how it works for you.

cheers
Wendy

[Rattrap]

well job is done & i think we are due for a frost tonight by the look of the sky so tomorrow will tell.
If it doesn't work the next move will be a full false ceiling. At $40 for bitumen black & a brush plus half a days labor was worth a try for sure.

[marri334]

rat im a ranbuild installer in western australia so not as cold as tasmania but down here in pemberton it does get a bit chilly. anyway being a full time shed erector and carpenter ive got to ask do you have a membrane under your roof sheets as that will make a difference ,i think its to do with temperature differential .also the membrane actes as run off and discharges the condensation down hill as it were ,if you do have it im a bit confused as to why it drips off your rafter but not your sheets.for a membrane you can use sisalation commonly called paper here or aircell /insulbreak a bit dearer but very effective it would mean ripping your roof off but better that than damaging a beautiful piece of furniture anyway hope this helps no problem if it doesnt cheers steve:U:U

[Rattrap]

Steve yer my shed has sisalation installed & the tar idea didn't work. big fat drips this morning.:C:C:C

[Yonnee]

I'm intrigued by this as I'm in Melbourne, and have had sisilation in both my sheds with no drips, whereas the pergolas and carports without it, drip like crazy.

Is your shed fully enclosed? I notice the large opening to the left of the fireplace, does that have a door?

[Rattrap]

Hi Yonnee, my shed is fully enclosed.
It has 2 roller doors in one long side & a standard door in 1 of the ends. It also has 4 'clear' fiberglass panels in the roof. There is however quite a gap between the top of the roller door & the top of the roller doorway - horizontally not vertically. The shed is all steel with a concrete floor & is 6m x 15m i think. . As i mentioned earlier it has full sisilation over the entire roof except where the skylight panels are. The sisilation is sandwiched between the roof iron & the C section trusses with box wiring holding the sisilation in place across the entire roof. I had to cut thru some of the sisilation to install the woodheater & it looked like 2 sheets of alfoil sandwiching a thin layer of tar.
The shed doesn't leak at all when its raining, only when its fine & we have a frost & then pretty much along the entire length of the rafters.
I'm hoping that once i get busier in the shed the wood heater will keep enough warmth thru the night to ease the problem. In the meantime its tarps over everything. :doh:

[marri334]

very confusing will ask around:?

[Wood Borer]

Rattrap,

I have foil backed wool insulation on my roof and the roof is at a 22 degree pitch and no problems so far.

I am guessing that we have a similar climate to you, lots of frosts and snow during winter.

Is it possible that the clear panels are the source of the problem?

It must be extremely disappointing having to tarp everything every cold night.

[marri334]

as mentioned before im a shed builder and skylight panels have heavy condensation more so than zincalume sheeting are your skylights near the rafter?

[Yonnee]

I had a strip of skylight in my first shed, and it was the only place it dripped. Current shed, no skylight, no drips.

[Yonnee]

Oh, and I love the heater. Did you buy it or build it? I might just have to "borrow" that idea... I have a couple of 44's lying around.

[ian]

Steve yer my shed has sisalation installed & the tar idea didn't work. big fat drips this morning.:C:C:CI wsa going to ask how the bitumen was supposed to work

to stop the condensation freezing on the steel I think you'll have to wrap insulation arround the steel

[Rattrap]

Thanks for dropping by with your thoughts guys, its much appreciated.
There are only 3 skylight panels not 4, they run the full width of the shed so they go over all 4 of the steel rafters. I haven't really noticed any concentration of drips under the skylights, it seams spread pretty much along the full length of the rafters. I'm not sure how i would determine if the skylight panels are the actual culprits. Could i throw a few blankets over the skylights at night just as a test??? Tho i'm not sure the wife would be all that pleased! :q
I'd be prepared to replace the skylight panels if i knew for certain they were the cause of the problem but i would miss the natural light from them. Tho on an overcast day in winter they don't do much at all.
Ian i had thought about wrapping the rafters with some sort of inulation but because the roof sheets sit right on the rafters that would mean lifting all the roofing sheets - not a job i'm keen to tackle.
Yonnee i bought the heater per assembled but you can buy the door, flue & leg pieces as a kit & do it yourself. They are quite popular here. We get about 6 years out of the drum on average before it burns out depending on usage then u just unscrew the kit & mount it onto a new drum & away you go again.

[Wood Borer]

The slope of your roof looks a bit "tame" to me, I wonder if that is a contributing factor?

Here's a photo of my roof at 22 degrees pitch.

[Rattrap]

Looks like very similar construction Wood Borer but yer very different roof profiles. I wouldn't have a clue if the differing roof profiles could contribute to the problem.
- no frost last night, no drips......

[Rattrap]

Quick update, we had a very heavy frost last night which was actually a good thing in conjunction with the newly applied paint on tar black because it showed clearly just where the drips were coming from & you guys were correct, it appears that the worst of the drips are coming from the areas where the skylights are.
The big question then is what can be done about it? I have no internal lighting at this stage - on the important things to do list - & so naturally i have my tablesaw & my main assembly bench directly under skylights.....
I'd really rather not remove the skylights but then i really do want to be done with these drips. 1 thought i had was to lift the skylights & wrap the steel rafters under them with some form of insulation, not sure if that would help tho....

[hitch]

Quick update, we had a very heavy frost last night which was actually a good thing in conjunction with the newly applied paint on tar black because it showed clearly just where the drips were coming from & you guys were correct, it appears that the worst of the drips are coming from the areas where the skylights are.
The big question then is what can be done about it? I have no internal lighting at this stage - on the important things to do list - & so naturally i have my tablesaw & my main assembly bench directly under skylights.....
I'd really rather not remove the skylights but then i really do want to be done with these drips. 1 thought i had was to lift the skylights & wrap the steel rafters under them with some form of insulation, not sure if that would help tho....

Rattrap I live up the road a bit from you at Port Sorell. I probably don't get quite as many or as intense frosts as you however our sheds appear to be very similar but I don't have any problems with condensation. The most obvious difference in our sheds appears to be the pitch of the roof. Perhaps the lower pitch of your roof is not allowing the condensation to drain away.

A pic of my shed's roof is attached.

[Rattrap]

You could well be right Hitch. wood borer suggested the same. Tho its not like theres a lot i can do about that issue.... I'm now thinking its more connected to my skylights as that's where the majority of the drips were this morning. Although you have skylights Hitch & no drips. hmmm. Your skylight sheets are a polycarbonate by the look of them where as mine are the older fiberglass sheeting. They're not clear like yours but do let it some light. I wonder if that can play a part?

[marri334]

fibreglass does condensate more than poly but the issue is the skylights have to go your options for light are electrician obviously, make some windows yourself using the tools in your shed or go with the aluminium variety and a third one that is little used is to put skylights in the walls. for security reasons you only need to go above the last wall purlin ,and you can reuse the roof skylights if they are in good nick. replace the roof sheets and insulate. the workshop where i sub contract from has skylight in the walls and they let heaps of light in

bitumining the rafter or even insulating it wont stop the water dripping on the rafters so any more efforts there wont help good luck steve

[Rattrap]

I think you are right Steve. I think my next move should be to replace the skylights & wire in some lighting. That means its going to have to wait a few months tho. I'll have to look into putting windows in the north facing wall.

[Yonnee]

Have you ever sat under a pergola with clear or even tinted roofing on a hot day? It is almost unbearable. The same goes in your shed with those silly "skylights". I've been working at a bench with the sun belting through the "skylight" on the back of my neck and I had to move for an hour or so till the sun moved over. I vowed never to have these in any of my sheds again. And windows are asking for trouble from those light fingered bastards that think they need your stuff more than you do. If you really feel need for natural light, then as Steve had suggested, use the skylight material, and add it to the top 12 inches of your walls. You might need some extra wall purlins to make it work.

[Rattrap]

Thanks Yonnee, yer i tend to agree with you on the subject of clear sheets. The semi clear sheets i have now are quite good thru the summer, they throw down heaps of natural light without all that heat. On a cloudy day they're not of much use tho, thats when the indoor lighting is needed badly.

[Graziano]

I have a corrugated colourbond roof laid over foil backed insulation and supported by 200mm purlins. Because I live in the tropics, the shed traps cool air during the night and at sunup the roof has condensation forming on top with enough forming to fill half a bucket (9m x 4.8m roof).

I've only seen this phenomenon on insulated roofs, uninsulated has no condense as there's no cool/warm differential, in your case warm shed, cool outside air and in my case warm outside air, cool shed. All I can suggest is another layer of insulation around the purlins as they are a thermal leak to the outside air via the squashed insulation and must be at a lower temperature. you could experiment with taping some insulation round a section of purlin.

Hope this helps.

[Rattrap]

I haven't gone any further with fixing this problem just yet tho i was speaking to a guy at the local hardware store that only works there once a month & he has seen the exact problem & found the best fix for it is a second sheet of laser light over the existing sheets but with a narrow spacer to create a small air gap.
He says that this way the frost can't fall on the bottom skylight sheet, if it can fall on it, it can't freeze any moisture in the air onto the steel rafters.
He also said that the lower the pitch of the roof the worse the problem can get which fits in very nicely with exactly what has been said in this thread.
As you can imagine i'm very keen to get this fixed but i've got a couple of projects on at the moment that are sucking up all my limited attention so for now this problem has been pushed to the back of my mind. Stay tuned tho as i plan to try this method over 1 skylight in the next few weeks.

Graz, it sounds like the problem is completely reversed in the tropics. I did briefly consider adding insulation around the steel rafters however that would also mean lifting the entire roof sheeting - no thanks.
Jacky, the door to the left of the drum heater is a roller door for the car, its always kept closed when not in use. I've pretty much nailed down the cause of the problem, theres a couple of main culprits - skylights & a low pitch roof - tick, tick. :doh:
Just as soon as i can get round to ordering a sheet of Laser Light & get a dry weekend i'll give this fix a try, won't take long to get a result we are having heavy frosts pretty much every night now.

[Harry72]

I get this problem too on the flat lean to roof at the rear of my shed, the main shed roof (22° gable) doesn't drip. My new shed has Permastop insulation I havent seen any drips yet.

[Rattrap]

I had to do a search to see what permastop insulation was, looks like good stuff - foil sisilation with a pink batt layer. Wouldn't help my issue however as its only under the skylights that the condensation occurs, elsewhere the standard sisilation does the job fine.

[appiwood]

Hello Rattrap, not sure how / if this helps, last week I was at a training seminar ( I'm a NSW builder ) one of the speakers was spruiking a product that was widely used in the USofA and NZ to combat " sick home syndrome ", it had an extremly R value but also doubled as a moisture barrier.

You will get condenstion whenever the temp' differential is 8 degree ( or more ) the moisture on your battens - or any section is coming from within the building, not as falling frost, I'm guessing the best longterm fix would be to lft the roof sheets ( as has been suggested ) and to increase the insulation, I think if you paint the steel with bitumen or anything you will still have the problem, another suggestion would be to do what the poms do and run a de-humidfyer ( sp???), if the skylights in the roof are a problem, is it possible to change them to North facing wall ones??.

Good luck with it, there is nothing worse than rusting tools.

[Rattrap]

Thanks for your input Appiwood. At this stage i still plan to try the second sheet of clear over the existing skylight panels as that appears to be both the cheapest & best chance of fixing the problem. If it doesn't work then i'll replace the skylight outright with some steel sheets & add some sisilation to where the skylights were.

[Warb]

Condensation is caused because warm air can hold more moisture than cool air. So when warm/moist air is cooled by contact with a cold surface, condensation forms as the air deposits the moisture it is no longer able to hold. How much condensation depends on how much moisture the warm air contains. Unfortunately warm air rises, contacts the cold roof of the shed, deposits it's moistures then the now cold/dry air falls and is replaced by more warm/moist air. Whether the condensation forms drips then becomes a function of the shed:

1/ My workshop is all steel, skillion roof, unlined and uninsulated. The concrete floor has a DPC and so is dry, there is no wet timber, so the air is quite dry. The shed is unheated and fairly drafty, which from another viewpoint means "well ventilated" (and cold). The small amount of condensation that may form (I've never looked!) on the roof never gathers in sufficient quantity to form a drip.

2/ My "hay" shed is all steel, exactly the same materials as the workshop (but far bigger). However it has only three sides, a gable roof and a dirt floor. The air is moist because of the dirt floor and the floor is "warm" because it's under cover, the shed roof traps the rising warm/moist air and the cold steel frame causes condensation (warm air cools, deposits moisture then falls to be replaced by more warm/moist air etc.). The condensation runs down the iron to the next purlin, then runs down the purlin and drips to the floor. There is a dripline below each purlin.

3/ I have a 40' shipping container. This has a suspended wooden floor with wet dirt beneath (it was recently moved so the dirt beneath has not had time to dry out). It is all steel, with the normal square section corrugated walls and roof, no leaks but no ventilation. It RAINS in this shipping container. The problem is that through the day the air warms up, as does the ground below the container. When the roof cools, the warm/moist air cycle happens to a massive degree, producing an almost unbelievable amount of condensation......

To fix the problem;

prevent condensation by stopping the warm moist air from meeting the cold surface i.e. insulate the steel to remove the contact with warm air

or

prevent warm moist air from meeting the cold surface by removing the warm moist air - ventilation and COLD SHED!

or

prevent condensation by keeping the air in the shed dry, so it has no moisture to deposit i.e. seal the floor if it is damp, don't keep items that release moisture (wet timber, washing etc.) in the shed

or

if none of the above is possible (or desirable), then accept that condensation is inevitable but channel it to where it can do no harm i.e all condensation forming steel surfaces needs to slope sufficiently that the drops run along to points of your choosing, rather than dropping off over the machinery!

Which approach will work depends on the situation!

Note that if you have a damp floor, damp timber etc. in the shed, and then you warm the air with a heater it will likely pick up more moisture, so unless you produce enough heat to keep the steel frame warm (very hard to do) your problems may get worse not better!

There is a thin "foil backed foam insulation" product, designed to be stapled to the joists underneath houses (houses on piers!). It's rated R1 from memory. You could probably run such a product across the bottom of the purlins, secured to the purlins with screws or battens, and sealing the joints with duct tape. This would trap a layer of air between the roof iron and the insulation, and prevent the warmer air below from meeting the cold shed frame....... Done right (i.e. trap the air when it's dry!), this may well be your best bet.

[Rattrap]

Thanks Warb, plenty to think about there! :2tsup::2tsup:

[Jack E]

This is a good thread for me Rattrap, I have just bought shed very close to you so I have some good points to consider, cheers.

[pjt]

I am wondering if the roofing screws would transmit enough of the cold from outside to the inside, as Warb has said hot moist inside meets cold and that's where the first bit of condensing happens and then over the night enough for drips, it might not be the rafters so much as the roofing screws transmitting the cold to the rafters, Are there umm :doh:(painted now) Where there localised areas of the white corrosion inline with the screws? If so maybe a bit of expanding foam squirted on each screw (inside) just thinking that u might not have to do the whole rafter if you go that way, What do you think?


Pete