Metal roofs - black, white, need plywood underneath?

[jennyinvermont]

So we have a great plan for a coop we're building. We're swapping out the shingles for a metal roof (way cheaper, and easier). We've mostly heard we DON'T need the plywood under metal roof, but that seems weird to me? Won't hte plywood kind of seal the roof? But no plywood would add ventilation? We're thinking of doing a black roof but I feel like we NEED plywood underneath to block the heat? (We live in Southern Vermont, humid in summer but mostly really cold). Oh and yes, we're extending the roof - by ??? 3 inches on each side? Any recs?

 

[3KillerBs]

No plywood necessary with metal. That's one of the advantages and cost savings.

However, you will NEED generous soffit and ridge/gable-peak ventilation or humidity from the chickens' breath and poop will condense on the metal and cause it to rain inside (probably contributing to frostbite in your climate).

While you have the roof off anyway, you might modify it to add a monitor or cupola to ensure good airflow.

Some people find it necessary to insulate the underside of metal roof and others don't.

 

[CluckerFamily]

I put plywood under my metal roof due to the winters we get in Wisconsin.

 

[jennyinvermont]

I put plywood under my metal roof due to the winters we get in Wisconsin.

did you put anything between the plywood and metal? felting, etc? do you have any problems with condensation?

 

[Silexian]

So we have a great plan for a coop we're building. We're swapping out the shingles for a metal roof (way cheaper, and easier). We've mostly heard we DON'T need the plywood under metal roof, but that seems weird to me? Won't hte plywood kind of seal the roof? But no plywood would add ventilation? We're thinking of doing a black roof but I feel like we NEED plywood underneath to block the heat? (We live in Southern Vermont, humid in summer but mostly really cold). Oh and yes, we're extending the roof - by ??? 3 inches on each side? Any recs?

You do not need plywood underneath. I would highly recommend insulation under the metal though.

 

[Silexian]

did you put anything between the plywood and metal? felting, etc? do you have any problems with condensation?

When I put a metal roof on my house. The metal supplier recommended 30# felt paper over the plywood. 15# is what is normally used under shingles.

 

[SueT]

Our coop is an old metal shed with wooden front. No plywood under the metal. It has been fine, we’re going on 6 years.

 

[CluckerFamily]

did you put anything between the plywood and metal? felting, etc? do you have any problems with condensation?

I just installed closure strips on the top and bottom of the plywood before laying the metal roof. I wanted to prevent hornets from building under the roof.
I have no condensation problems.

 

[robherr]

I have a metal roof, used strips of wood as reinforcement rather than solid plywood

 

[U_Stormcrow]

Metal Roof - I'm not fond of colored, but I have different climate concerns than you do, set upon purlins (basically, thin wooden boards run on top of, and perpendicular to, the rafters). No decking underneath.

The airflow ensures there are limited condensation concerns between thermal gradients (the whole reason felt paper is placed between plywood decking and the actual waterproofing, whether shingle or sheet metal or polycarbonate.

Placing decking increases costs and traps moisture, while preventing visual inspection so leaks. Placing sheet metal essentially directly on plywood (or on purlins, attached to plywood, as when placing sheet metal over an existing shingle roof at end of life) creates no significant dead air space to work as insulation - the purlins are typically only 3/4" thick. That's not much dead air. Metal roofs open from underneath can be leak checked easily and routinely so when they appear, can be corrected early while they are small.

If the underside of your soffits are opened up as free ventilation, and you use a ridge vent, monitor roof, or similar design to allow air to escape at the top, you create a passive ventilation system that draws cool air from lower/shaded locations, warms it as it passes across the underside of the roof, and escapes at the top - which also draws moist, ammonia laden air from the coop.

That said, ridge vents are shallow, and easily plugged by inches of snow - a condition monitor style roof designs address quite well. Not that they are required - you have to look at the total airflow/ventilation package for that - but they do solve a lot of problems (or no one would waste the time and materials building them, except for reasons of aesthetics)

You can also do a half monitor roof, open facing away from prevailing winter winds, if you are looking for a slightly easier, slightly less resource intensive build - but its really not a big difference.