# metal roof. Lathe?



## Stan ETenn (Feb 9, 2005)

We're ready to recover our church with 29 gauge metat roofing. We're getting different opinions about the necessity of lathing under the metal roofing. One wants to strip the old roofing, refelting and installing the metal roofing. Another wants to install lathe and then the metal roofing. We appreciate any input. Thanks 3/4 in. 1" X 4" Lathe


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## Grumpy (Oct 8, 2003)

What type of roof do you currently have?

Most roofers prefer stripping. I personally wouldn't put a metal roof over another layer of roofing.

If you don't strip the roof then the lathes/furring strips will provide a more even surface to place your new roofing panels on, and provide a air space under neath for ventilation.


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## pgriz (Sep 29, 2003)

Grumpy said:


> What type of roof do you currently have?
> 
> Most roofers prefer stripping. I personally wouldn't put a metal roof over another layer of roofing.
> 
> If you don't strip the roof then the lathes/furring strips will provide a more even surface to place your new roofing panels on, and provide a air space under neath for ventilation.


I'm with Grumpy on the stripping.

As for ventilation, the creation of air compartments under the metal roofing using horizontal lathes, does not constitute ventilation as the air compartment need to be joined vertically to allow air movement by convection. The usual way to achieve that is to install vertical lathes first, then the horizontal ones. Of course, you have to provide for intake air (at the soffit) and for outlets (usually at a ridge vent).

The lathes also serve the purpose of allowing the metal to expand and contract without causing extensive stress on the metal at the fasteners. Without the lathes (or strapping, or furring as these are called in various parts of the country), the expansion and contraction of metal will cause the screws to push at the top and bottom of the panels, eventually creating oval holes which can leak. Oh, and we speak from experience on these...


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## DBS01 (Mar 4, 2005)

*installing lath (stripping)*

we as a rule will not remove the existing roofing materials, you need to check on your local codes. one thing we would reccommend is using a "condensation blanket" under the stripping, we use a foil/bubble/foil product under the stripping, this gives you a radiant energy reflector reducing attic temps and gives you additional winter insulation. we have installed roofs this way for 10 years and have seen no adverse efffects.

ventilation is still required in the attic space as normal but in that 3/4" air space the trapped air will not result in problems.


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## Grumpy (Oct 8, 2003)

DBS01 said:


> we as a rule will not remove the existing roofing materials,



I will be the first to admit I know very little about metal roofing. I will also state that this above statement goes against everything i have ever heard from many many many successful roofers.

I as a rule ALWAYS want to remove the existiung roof and ONLY leave the roof in place if the customer forces me to.


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## darryl (Mar 10, 2005)

Tear that sucker off, check out the deck and use a min of 26 ga. metal, 24ga if you have the extra couple of bucks .


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## AaronB. (Oct 6, 2004)

HOW ABOUT....The radiant barrier will provide extra insulation, as long as you vent the attic?!?!?!?!?!?!?!?!


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## pgriz (Sep 29, 2003)

Grumpy, most of the metal roof manufacturers claim on their web sites that you don't have to strip. The contractors who install their products are happy to tell this to the customers, so that the price differential between metal and asphalt is lower. Personally, I think this is cheating the customer, since this leaves the old material up on the roof (adding weight, etc.), and the stuff continues to deteriorate (heat/cool/oxidize even with no UV), so underlying the "permanent roof" is a layer of debris. You can't really use I&W, since that needs to be adhered to the deck, and you never know if you have rot. My customers depend on me to tell them the right way to do stuff, and they pay for it. If they cannot afford to do it right, then we won't do it for them.


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## Grumpy (Oct 8, 2003)

I've found manufacturers give the minimum allowed installation techniques. O see your point Paul, and I trust your insight.


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## red_cedar (Mar 30, 2005)

This ones a little old, but would like to add to the post.
IMO. The old roof, depending on how many layers, or type, does not NEED to come off. What one should realy be looking for is a solid fastening point for the new roof. 
I cant tell you how many times I have seen recovers with a good material last many decades with no apparent affect on the old roof. What works in real life may not work to ones perfect ideals. Tearing off is the most thoughoy way to go but not absolutly nessecary, though each situation ( roof ) is different, And any roofer who isnt trying to get more labor out of the job will tell you that. 
With all the solid deck metal roofs compared to lath applications.and that are up and have been up for decades we should expect to see them fail soon by some peoples standards. The older decks many times where some form of solid sheating
I think its funny about the comment of the manufacturers, most roofers dont even follow manufacturers recommendations. For example go look at how the nails are placed in a simple asphalt shingle application,then say if manufacturer guide lines are followed exactly or close. I believe manufacturer recommendations are guide lines that are shown to work for there product . Of course they are a minimum, everything can always be improved apon.
One could go look at the copper and common sense book and improve on that as well.


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## Doofus Emeritus (Dec 18, 2004)

Hmmm.... Other considerations may come into play as to why one guy says recover. If the existing roof is composition, then furring strips and metal will keep the roof at a Class-A fire rating. Most people are under some delusion that metal roofing is Class-A. Actually, metal falls under Class-C over combustabile decks. Check with your local building dept. over what the fire rating should be. If your district requires Class-A, then your church will save money by recovering. Another alternative would be to strip the roof, inspect the substrate for damages and fastening, then add a Class-A underlayment before installing the metal.

As for 29 GA metal, I'm shaking my head at that one. What matters is the decimal thickness of the metal. The nominal decimal thickness for 29 GA is .0172 with a high end of .0202 and a low end of .0142. Rarely have I seen metal roofing delivered on the high, or nominal end. It's usually on the low end. Lets put it this way, 29 GA is really thin. Get a sample of the metal and put a micrometer to it. I would be interested in looking at the panel profile and manufacturer your roofer has specified for the job.


Best regards,

DE


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