# Metal roof question



## Krich (Jul 25, 2017)

Our house has a metal roof... and we are in the south where it gets really hot so during the day we hear these popping sounds fairly frequently.  Sometimes more frequently than others.

I got to thinking that it's gotta be the metal roof expanding since heat expands since there is no other activity going on in or around the house that could be causing this popping sound... and it only happens during the heat of the day.

The house only has openings on each gable end for air flow, so I'm thinking since hot air rises a logical fix for this is to take the top cap off the runs the length of the house and replace it with a cap that is vented.

Does this sound like something that would work so the hot air can have a way of escape?

If so, any recommendations on where to find a vented cap that is made for metal roofs that I assume is secured using self taping screws?


----------



## nealtw (Jul 25, 2017)

Yes that is called a ridge vent, you also need soffet vents to get real good airflow. It would be really hard to say how effective it is for cooling the house but it is good for the structure to have good venting.

Oldog will likely be along for advice about the ridge vent.


----------



## Krich (Jul 25, 2017)

There are air vents on each gable end so I was hoping a ridge vent on top would provide a way for the hot air to escape.

Do you think additional vents would be need in addition to the ridge vent on top?


----------



## nealtw (Jul 25, 2017)

Krich said:


> There are air vents on each gable end so I was hoping a ridge vent on top would provide a way for the hot air to escape.
> 
> Do you think additional vents would be need in addition to the ridge vent on top?



If hot air rises right now the gable vent will cool to the level of the top of the vent so air above that would be hotter. So the ridge vent is good for taking the hottest air out. 
Bot now the air will be pulled from the gable vent and discharged from the ridge vent.

The heat below the vent will have to rely on the weather system inside the attic for the heat to rise and mix with the moving air above.
So venting from the soffet uses the heat rising idea to the most benefit.


----------



## oldognewtrick (Jul 25, 2017)

You should intake air at the soffit and exhaust at the ridge. Having gable vents will short cycle the natural vent cycle. The air will circulate from the gable to the ridge and not draw out air lower in the attic.  Close off the gable vents with heavy mill plastic. Are there any existing soffit vents?


----------



## oldognewtrick (Jul 25, 2017)

And yes, the popping is the metal expandi,g and contracting. A 100' run of metal will expand over an inch when thermal cycled.


----------



## Krich (Jul 25, 2017)

> Are there any existing soffit vents?



No, there are not.  These can be installed in the overhang on the edge of the house, right?

I've seen these there on other houses come to think of it.






> And yes, the popping is the metal expanding and contracting. A 100' run of metal will expand over an inch when thermal cycled.



Does all this movement eventually damage the metal?

Any recommendations on where to find a vented cap that is made for metal roofs that I assume is secured using self taping screws?


----------



## nealtw (Jul 25, 2017)

Krich said:


> No, there are not.  These can be installed in the overhang on the edge of the house, right?
> 
> I've seen these there on other houses come to think of it.
> 
> ...



Maybe the better question is what do you have under the eaves of the roof . do you have an over hang. If there is plywood or other solid surface is it level or does it follow the slope of the roof.


----------



## Krich (Jul 25, 2017)

There is an over hang and it is level.  It appears to be maybe quarter inch plywood that I could cut with a jig saw. 

I could easily install vents.  All I would need to do it make sure they are centered in between the rafters.

How many vents would be needed in the over hang?


----------



## nealtw (Jul 25, 2017)

Krich said:


> There is an over hang and it is level.  It appears to be maybe quarter inch plywood that I could cut with a jig saw.
> 
> I could easily install vents.  All I would need to do it make sure they are centered in between the rafters.
> 
> How many vents would be needed in the over hang?



If the plywood is level then there would be a common area above it so being lined up would not be important. I am not up on how many sq inches you would need most times it is just vented soffet instead of the plywood. I am sure there are charts for it.


----------



## Krich (Jul 25, 2017)

I've seen houses that have a vent place in every other section in between the rafters.

So, is this one of those things where I'm going to have to measure the square footage of the attic and do some math to figure out how many vents to put in?

I can see the science in that... I just wonder how many roofers actually take this approach.

I spent some time in my younger years working for several remodeling companies where we did all sorts of work including roofing and they wasn't anything scientific going on at all other than the boos man guessing


----------



## nealtw (Jul 25, 2017)

Here you go all you need is width and length of house.
http://www.gaf.ca/roofing/residential/products/roof_vents/ventilation_calculator


----------



## Krich (Jul 25, 2017)

Good, thanks!

In the meantime before anything gets done... does the excessive heat moving the metal damage it at all?


----------



## nealtw (Jul 25, 2017)

Krich said:


> Good, thanks!
> 
> In the meantime before anything gets done... does the excessive heat moving the metal damage it at all?




It is not like the whole roof moves sideways, each panel will grow a little, it will be designed to take that movement.


----------



## Krich (Jul 25, 2017)

OK, I just wanted to know how much of an emergency this should be considered to be...


----------



## oldognewtrick (Jul 25, 2017)

What type if metal roof panel do you have exposed screws or hidden fastners/standing seam?


----------



## Snoonyb (Jul 25, 2017)

Attic venting is stated as 1/300 of the area, where underfloor venting is 1/150.

Where you have finished soffits, it's not just a matter of cutting a vent into the finished surface of the plywood, there must also be rafter blocking that will allow that venting to migrate into the attic.

Which may already be there and sometime in the past, covered up by the finishing of the soffit, so it could be in your interest to remove a piece of the finished soffit to find that out.

A ridge vent, while a long term benefit, may not relieve the metal expansion and contraction.


----------



## Krich (Jul 25, 2017)

oldognewtrick said:


> What type if metal roof panel do you have exposed screws or hidden fastners/standing seam?



Not sure, I'll have to get up there and see in the next few days...


----------



## oldognewtrick (Jul 25, 2017)

Take a picture of the panel, ridge and soffit, it will answer a lot of questions I don't have to ask


----------



## buffalo (Jul 26, 2017)

I have a metal roof , I did not personally install it . I have installed standing seam roofs . I just sided part of my house standing on the roof on a hot summer day. I heard the pops . A standing seam roof has concealed fasteners that allow the metal to expand and contract . 

The roof I have , and most have , and is a whole lot cheaper , is exposed screws. The screws go directly through the metal a d I to your structure .

All metal expands and contracts no matter what system . What I'm told is the movement pulls the screws back and forth , which ruins the rubber grommets and causes potential leaks . A standing seam roof does not directly.do this . Guess I'll see . But they are 3x more expensive . I'm guessing I'll be just fine .


----------



## oldognewtrick (Jul 26, 2017)

Buffalo, when the time comes, remove the screws and replace with the next size bigger.


----------



## slownsteady (Aug 3, 2017)

I know that I'm late to the party but the expansion of the metal has more to do with absorbed radiant heat than hot air. A piece of metal sitting in the sun gets hot and will expand despite the air around it. I don't know enough about metal roofs to make a judgement, but it is possible that the fastening system isn't right....or that the popping sounds are 'par for the course'.


----------



## grahamd (Aug 16, 2017)

Krich said:


> Our house has a metal roof... and we are in the south where it gets really hot so during the day we hear these popping sounds fairly frequently.  Sometimes more frequently than others.
> 
> I got to thinking that it's gotta be the metal roof expanding since heat expands since there is no other activity going on in or around the house that could be causing this popping sound... and it only happens during the heat of the day.
> 
> ...



As you said, the popping noise is the metal moving with the heat. Per previous comments, I'd recommend having both ridge vents and soffit vents to ensure you're getting maximum air flow, which will help to keep the metal cool and prevent movement (perhaps not entirely but excessively, at least). If you're looking for vented caps for metal roofs, I'd recommend giving a local metal roofing supplier; tap 'metal roofing [location]' into Google, and you'll find a local supplier. Typically, you shouldn't experience any problems ordering some for pick up.


----------



## voyager (Aug 24, 2017)

As usual, I'm chiming in very late and responding just to the OP.

Every morning I take my 1st cup of coffee and go out on the back lanai to drink it and give the cats their regular morning massage. About 8am, as the sun comes over the albezia trees to the east of us, and begins to shine on our roof, the popping sounds begin without fail. It took me a day or two to figure out what it was, the metal roof expanding from the heat from the sun building up. The noise is disconcerting if you don't know what it is. But, it is a normal thing for any metal roof and is not an indication of any problem by itself. The popping happens as the metal heats up and expands, which is before the area under the roof begins to heat up.


----------

