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house92 04-18-2011 06:42 PM

Metal roof/ ridge vs flat
I'm considering a new metal roof on the house(it currently has shingles) and notice that the latest trend is to nail or screw the roof in the flat instead of the ridge. I don't think this makes sense if you plan to keep the roof as long as the metal will last.

I asked a roofer to explain why the flat is the best he gave some reason that I don't remember. I asked what happens when the rubber washer rots from around the screw and he said, "Well, it will probably be time for a new roof." I thought, are you kidding? There is no time for a "new" metal roof unless it is damaged. We have metal roofs on our barns that have been there for 50 years, all nailed in the ridge. All they need is a coat of paint about every 8-10 years. For some unknown reason, there are a few random nails in the flats, and those are the places that give leak problems.

My theory is this: Nailing in the flat is quicker and, therefore, better for the installer. For support, some idea has been developed as to why screwing in the flat is better, but i don't buy it. It might be possible that it will last as long as people will "want" the roof. I realize that people these days replace things long before they "need" replacing just because they want something different.

But, if I want the roof as long as the metal will last, which will be years and years, wouldn't putting screws in the ridge make more sense?

oldognewtrick 04-18-2011 08:39 PM

The rule of thumb is to nail through the top of the rib and screw on the flat. Screws pull down tight and can cause the ribs to dent. A screw will seal better to a smooth surface. The neoprene washers will fail in about 7-12 years and can be replaced with bigger screws. Screw down panels are not meant for application on residences, they are meant for agricultural installations (barns).

If you must use exposed fastener panels on your house be sure to use a quality, high temp underlayment like Tamko Metal and Tile. Its a peel and stick membrane similar to Weather Watch with a high melt point.

Also..why do you equate quicker with better. Screws hold a lot better than nails, even ring shank nails.

house92 04-20-2011 04:53 AM

I meant that "quicker" was better for the contractor putting it on. faster means more money for him.

oldognewtrick 04-20-2011 05:17 AM


Originally Posted by house92 (Post 56256)
I meant that "quicker" was better for the contractor putting it on. faster means more money for him.

I agree, time is money in the construction trades. When we put on screw down panels we first mark on a panel a line where all the screws will go, then lay that panel on top of the stack of full sheets. Then we predrill all the full sheets at the same time. This saves a LOT of time on installation and keeps all the screw heads in a uniform, straight line.

Once again, if you go with screw down panels, I cannot suggest strongly enough to invest in a quality underlayment made for metal roof installation...and be sure if you presently have shingles to remove them prior to application of the metal. I see a lot of installers save time by installing a wooden batten and going over the shingles that are on the roof. This will severely shorten the lifespan of the metal roof installation. Trapped air will cause condensation and the moisture will rot the battens. You want the metal in contact with a hard surface not installed over an airspace.

siriuschaos 04-21-2011 02:04 PM

This post may be a wee late but if i may add my 2 cents. Most roofing tin is designed either with a hidden fastening system or a rib fastened method. Screwing in the field or flat is okay in a siding installation but roofing is meant to be fastened at the rib for ultimate strength. If wind gets under the sheets it can be torn off quite easily when fastened in the flat. The ribs add rigidity to the steel hence fastening here is recommended. Also any warranty may be void if fastened incorrectly or with improper fasteners

6273909 07-04-2014 10:18 AM

My father helped me with my first investment home. We installed a metal roof and he insisted on putting the screws in the raised ridges. We pre-drilled the holes, several sheets at a time, using one sheet as a template. We used long screws and one would screw the screw almost touching the tin and the other would take a wrench and snug it to the sheet with a hand ratchet. We completely screwed one sheet before moving to the next. It has been over 15 years and not a leak. I purchased another investment home about a year later and my brother helped me install the metal roof. We installed it by the metal supplier's instructions, screwing into the flats. It was a little faster than the other way. Eight years later I had to replace all of the screws in the one that was screwed into the flats. Some were leaking and it was too hard to track them down so I replaced them all with larger screws. The first house has never leaked and the second house is staring to leak again! SCREW INTO THE RIDGES NOT THE FLATS! Be really careful not to bend the ridge.

I have concluded the metal moves with heat and cool and works the holes larger and the rubber gets hard. In the ridge this happens too but because it is elevated and water is not under pressure to enter you do not have the same problems.
In my dad's old barn the lead covers have come off some of the nails and you can see daylight looking from underneath, but when it rains no noticeable rain enters because it is nailed on the ridge. Manufactures must recommend screwing to the flats because it is so easy to over tighten the screws and damage the tin. Even if you over tighten just a little it will cause your tin to dis-form which can cause a gap at the overlap seams if you screw the edges to hold it and then come back and screw the centers.

Forget about the warranty! A friend's blue tin faded after about ten years and looks awful. He tried to get it covered under his 30 year fade warranty and they offered him a 15% discount off the cost of new tin purchased at MSRP. The price was actually higher than you could buy it for locally.

nealtw 07-04-2014 02:44 PM

6273909: welcome to the site.

zannej 07-06-2014 06:53 AM

The reason to NOT screw in to the flats is because of the water flow. If you screw in to the ridges and maintain the height, the water rolls off of the ridges more easily and seeks the lowest point. The flats will end up holding more water, debris, and leaves (if you have trees nearby). With the screws in the valley rather than the hill, they are more likely to accumulate water during snow and hard rain.

So, I vote for screwing in to the ridges (but being careful not to crush said ridges).

On a side note, the bolts can actually be nice to grip on to with your feet to avoid slipping when you have to clean the roof. (My house has a 400 year old oak tree looming above so it drops a lot of stuff down).

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