Cob: Metal Roofing

Yun Que yunk88 at hotmail.com
Thu Mar 6 08:48:34 CST 2003 

<html><div style='background-color:'><DIV>
<P><BR><BR></P>
<DIV>
<DIV></DIV>
<P>Cat here, looking forward to thatch information. </P></DIV>
<P> My current house has a tin roof that is still holding after 75 years with only a paint job.  The structure will only support the tin without further reinforcement.</P>
<P>It would be my suggestion that one might design roof support for max weight, skin it with what is within current budget, leaving you the option to change the roof later.  I plan to use used tin but will build for slate.  That way when the slate comes along I will be ready!!  </P></DIV>
<P><EM>for the good of all </EM>Cat<BR><BR></P>
<DIV></DIV>
<DIV></DIV>
<DIV></DIV>
<DIV></DIV>
<DIV></DIV>>From: Darel Henman <HENMAN at IT.TO-BE.CO.JP>
<DIV></DIV>
<DIV></DIV>>Reply-To: Darel Henman <HENMAN at IT.TO-BE.CO.JP>
<DIV></DIV>
<DIV></DIV>>To: cob list <COBLIST at DEATECH.COM>
<DIV></DIV>
<DIV></DIV>>Subject: Re: Cob: Metal Roofing 
<DIV></DIV>
<DIV></DIV>>Date: Thu, 06 Mar 2003 19:08:38 +0900 
<DIV></DIV>
<DIV></DIV>> 
<DIV></DIV>
<DIV></DIV>>Here's to correct some faults in what Shannon wrote about roofs, which 
<DIV></DIV>
<DIV></DIV>>we both have installation experience in. But she did not consider the 
<DIV></DIV>
<DIV></DIV>>thermal performance issues, which I will expand on. 
<DIV></DIV>
<DIV></DIV>> 
<DIV></DIV>
<DIV></DIV>> 
<DIV></DIV>
<DIV></DIV>>"Shannon C. Dealy" wrote: 
<DIV></DIV>
<DIV></DIV>> > [snip] 
<DIV></DIV>
<DIV></DIV>> > > But, steel is a dumb choice for a roof, just as corrugated metal is. 
<DIV></DIV>
<DIV></DIV>> > > Expensive and is a thermal bridge (very high thermal conductance). 
<DIV></DIV>
<DIV></DIV>> > [snip] 
<DIV></DIV>
<DIV></DIV>> > 
<DIV></DIV>
<DIV></DIV>> > Have to strongly disagree with this one, modern enameled metal roofs are 
<DIV></DIV>
<DIV></DIV>> > about the cheapest type of roof you can put on when labor and life 
<DIV></DIV>
<DIV></DIV>> > expectancy are figured in (50+ years), at least in this area (Oregon). 
<DIV></DIV>
<DIV></DIV>> 
<DIV></DIV>
<DIV></DIV>>This is not a corrogated metal or metal roof you are talking about 
<DIV></DIV>
<DIV></DIV>>above, but a manufactured enabled metal. The question was about a metal 
<DIV></DIV>
<DIV></DIV>>roof, not an enameled material. 
<DIV></DIV>
<DIV></DIV>> 
<DIV></DIV>
<DIV></DIV>> 
<DIV></DIV>
<DIV></DIV>> > They are also environmentally friendlier than most conventional / 
<DIV></DIV>
<DIV></DIV>> > non-natural roofs, since at the end of their life they can be easily 
<DIV></DIV>
<DIV></DIV>> > recycled. 
<DIV></DIV>
<DIV></DIV>>Not as easily as adobe tile and green roofs or thatches. A lot of 
<DIV></DIV>
<DIV></DIV>>energy is require to so call re-cycle it. 
<DIV></DIV>
<DIV></DIV>>Also there is a lot of junk metal coming out that contains a lot of 
<DIV></DIV>
<DIV></DIV>>metal refinery refuse and might contain heavy metal particles, which 
<DIV></DIV>
<DIV></DIV>>are reportedly bad for health. 
<DIV></DIV>
<DIV></DIV>> 
<DIV></DIV>
<DIV></DIV>> > As far as the thermal bridge aspect, this frankly doesn't make 
<DIV></DIV>
<DIV></DIV>> > sense, since it doesn't bridge to anywhere, the sheathing, roof support 
<DIV></DIV>
<DIV></DIV>> > structure, insulation, and vapor barrier, are all below the roof, 
<DIV></DIV>
<DIV></DIV>> > and more to the point, in most roof designs for modern houses, there are 
<DIV></DIV>
<DIV></DIV>> > actually vents to allow air flow between the outer most layers of the roof 
<DIV></DIV>
<DIV></DIV>> > and the insulation in order to prevent moisture build up (building code 
<DIV></DIV>
<DIV></DIV>> > requirement), this alone by-passes most of the insulation value that might 
<DIV></DIV>
<DIV></DIV>> > be provided by using a material other than metal. 
<DIV></DIV>
<DIV></DIV>> 
<DIV></DIV>
<DIV></DIV>>Since you couldn't make sense let me help you make sense. Any skin, 
<DIV></DIV>
<DIV></DIV>>like a roof, it will bridge heat to or from the inside of the structure 
<DIV></DIV>
<DIV></DIV>>the outisde air. Just as our skin does. Go outside on a very cold day 
<DIV></DIV>
<DIV></DIV>>and lift up a metal block or even a wrench. Put that down and pick up 
<DIV></DIV>
<DIV></DIV>>a piece of wood. You'll notice the difference is great. The metal 
<DIV></DIV>
<DIV></DIV>>conducts or suck energy about a thousand times faster than wood. You 
<DIV></DIV>
<DIV></DIV>>would also never of course put on a metal jacket in the winter. But we 
<DIV></DIV>
<DIV></DIV>>will use layers of clothing to keep us warm. Metal roofs will also, 
<DIV></DIV>
<DIV></DIV>>depending on its emissivity factor radiate heat out at night. It will 
<DIV></DIV>
<DIV></DIV>>radiate it inside and conduct it inside during the day. 
<DIV></DIV>
<DIV></DIV>> 
<DIV></DIV>
<DIV></DIV>>Having insulation under it helps, but it pulls more energy out through 
<DIV></DIV>
<DIV></DIV>>the insulation that an less conducive roofing surface would do. Every 
<DIV></DIV>
<DIV></DIV>>bit of insulative material helps. Perhaps in somes areas where the 
<DIV></DIV>
<DIV></DIV>>weather is very moderate it doesn't mater. Local factors for a 
<DIV></DIV>
<DIV></DIV>>materials usage then come into focus. 
<DIV></DIV>
<DIV></DIV>> 
<DIV></DIV>
<DIV></DIV>> > The primary function of 
<DIV></DIV>
<DIV></DIV>> > the outer most layer of the roof (metal, shingles, tile, etc.) is to block 
<DIV></DIV>
<DIV></DIV>> > rain, hail, wind, etc. from going into the building from above and/or 
<DIV></DIV>
<DIV></DIV>> > damaging the underlying parts of the roof system, it's insulation value 
<DIV></DIV>
<DIV></DIV>> > is of limited value in most modern structures. 
<DIV></DIV>
<DIV></DIV>> 
<DIV></DIV>
<DIV></DIV>>This we know, but shingles and tile do not conduct thermal energy at 
<DIV></DIV>
<DIV></DIV>>anything like metal does. Tile and shingle roofs would transfer heat 
<DIV></DIV>
<DIV></DIV>>nearly a thousand times less than metal. Most modern structures you 
<DIV></DIV>
<DIV></DIV>>mention above are not designed well I agree with you. And no one should 
<DIV></DIV>
<DIV></DIV>>add additional burdon on the insulation in a roof but use a material 
<DIV></DIV>
<DIV></DIV>>that would or could even add to it. That is the best solution that can 
<DIV></DIV>
<DIV></DIV>>be found. 
<DIV></DIV>
<DIV></DIV>> 
<DIV></DIV>
<DIV></DIV>> > From the above and other 
<DIV></DIV>
<DIV></DIV>> > considerations (such as weight and the amount of structure required to 
<DIV></DIV>
<DIV></DIV>> > support it), metal comes up superior to three tab shingles, cedar shingles 
<DIV></DIV>
<DIV></DIV>> > and tile (and I have worked on all four of these roofing systems). 
<DIV></DIV>
<DIV></DIV>> 
<DIV></DIV>
<DIV></DIV>>You seem to be describing a very thin metal with an enamble on it. 
<DIV></DIV>
<DIV></DIV>>It's hard to see that it would be less weight that shingles or cedar 
<DIV></DIV>
<DIV></DIV>>shingles, though I haven't seen this conglomate item your mentioning. 
<DIV></DIV>
<DIV></DIV>>Even though it would pull energy through your insulation faster than a 
<DIV></DIV>
<DIV></DIV>>less conductive material would without a doubt. 
<DIV></DIV>
<DIV></DIV>> 
<DIV></DIV>
<DIV></DIV>> 
<DIV></DIV>
<DIV></DIV>> > Of course for a roofing system like thatching (another roofing technique I 
<DIV></DIV>
<DIV></DIV>> > have some experience with - and someday Mark I will finish that thatching 
<DIV></DIV>
<DIV></DIV>> > article - reeeaaal sooooon now :-) 
<DIV></DIV>
<DIV></DIV>> 
<DIV></DIV>
<DIV></DIV>>I am looking forward to that. I just visited several thatched roofs 
<DIV></DIV>
<DIV></DIV>>last week. 
<DIV></DIV>
<DIV></DIV>> 
<DIV></DIV>
<DIV></DIV>> 
<DIV></DIV>
<DIV></DIV>> > the above statements don't apply 
<DIV></DIV>
<DIV></DIV>> > because it is breathable, provides it's own insulation and there is only 
<DIV></DIV>
<DIV></DIV>> > one "layer" to the roof (though for fire safety purposes the interior 
<DIV></DIV>
<DIV></DIV>> > of the roof should be covered over to block most airflow to the underside 
<DIV></DIV>
<DIV></DIV>> > of the thatch). When all things are considered - cost, code, building 
<DIV></DIV>
<DIV></DIV>> > officials, strength and materials required to support roof, ease of 
<DIV></DIV>
<DIV></DIV>> > getting materials and experienced roofers for the particular style, as 
<DIV></DIV>
<DIV></DIV>> > well as environmental aspects - for many if not most people on this list a 
<DIV></DIV>
<DIV></DIV>> > metal roof is likely to actually be the best choice. 
<DIV></DIV>
<DIV></DIV>> 
<DIV></DIV>
<DIV></DIV>>If they want to spend a lot of money on heating and cooling, your 
<DIV></DIV>
<DIV></DIV>>right. But one must consider this as an ancillary cost. Cement might 
<DIV></DIV>
<DIV></DIV>>be even cheaper. Would you use it? Money is not the only factor to 
<DIV></DIV>
<DIV></DIV>>consider. 
<DIV></DIV>
<DIV></DIV>> 
<DIV></DIV>
<DIV></DIV>> > Of course for someone living out in a rural area of a third world country, with 
<DIV></DIV>
<DIV></DIV>> > significantly different costs for materials relative to their income, lack 
<DIV></DIV>
<DIV></DIV>> > of building codes, and greater availability of roofers experienced with 
<DIV></DIV>
<DIV></DIV>> > natural materials, a thatch, wood shingle, or other roof approach will 
<DIV></DIV>
<DIV></DIV>> > probably make alot more sense. 
<DIV></DIV>
<DIV></DIV>> 
<DIV></DIV>
<DIV></DIV>>True. Please finish that thatch article. There's little practical 
<DIV></DIV>
<DIV></DIV>>information out there on it. 
<DIV></DIV>
<DIV></DIV>> 
<DIV></DIV>
<DIV></DIV>>Darel 
<DIV></DIV>
<DIV></DIV>> 
<DIV></DIV>
<DIV></DIV>
<DIV></DIV></div><br clear=all><hr>STOP MORE SPAM with <a href="http://g.msn.com/8HMNENUS/2728">the new MSN 8</a> and get 2 months FREE*</html>