答复

1. 
   彼得·L|2017年3月14日下午10:52|#1

   I am in the same scenario as you except my application is with SIPS. My options have narrowed to: metal sub-girts which raise the metal roof either 1/2" or 1" from the substrate OR 1x3 wood purlins which raise the metal roof 3/4" from the substrate.

   The steel sub-girts provide a strength advantage since the standing seam metal roof clips onto the sub-girts. The 1x3's don't really provide any strength but provide the air channel needed.

   The question is HOW MUCH of an air gap is needed under the metal roof? Is 1/2" enough or is 1" required?

2. GBA Editor
   马丁·霍拉迪（Martin Holladay）|3月15日，2017年06:02 AM|#2

   Jacob,
   在佛罗里达州，在固体OSB或胶合板护套上安装所谓的“ 5-V压接”金属屋顶很常见（当然，在护套和屋顶之间有一层屋顶底层，但没有任何purlins或绑带）。在您的气候下，这种方法效果很好。

   -- Martin Holladay

3. GBA Editor
   马丁·霍拉迪（Martin Holladay）|3月15日，2017年06:05 AM|#3

   Peter,
   In the case of SIPs, it's essential (in my view) to have an air channel between the roofing underlayment and the metal roofing. The colder the climate, the more essential the air gap.

   If I had to choose between a 1/2-inch gap and a 1-inch gap, I would be inclined to go with the 1-inch gap if I were building in Climate Zone 5 or anywhere colder. In Zone 4, the 1/2-inch gap would probably allow me to sleep at night.

   -- Martin Holladay

4. 
   Jacob Felton|Mar 15, 2017 02:02pm|#4

   Thanks Martin for the excellent responses, as always. Peter, I'm glad you brought up SIPs because I have to confess I, I'm not sure whether I should treat a nailbase panel similarly. In other words, are there any fundamental differences between a true SIP and a nailbase panel over sheathing when in neither case the attic space is vented? If not, that implies I should treat a nailbase panel like a SIP and vent over it, even though installing metal roofing directly to a solid deck is acceptable practice in my area. Perhaps the answer is entirely dependent on the particulars, and in this case I would probably go with a 2.5"-3" nailbase panel yielding R-12-15 with about R-23 of fluffy in the rafter bays.

5. 
   彼得·L|Mar 15, 2017 10:43pm|#5

   马丁，

   I am in Zone 4B.

   If it were your home, would you go with the 1" spacing or the 1/2" spacing?

   The con to the 1" is that supposedly the 24 gauge panel can flex slightly under heavy snow loads since the OSB substrate is not sitting directly underneath the metal roof panel.

6. GBA Editor
   马丁·霍拉迪（Martin Holladay）|Mar 16, 2017 04:37am|#6

   Peter,
   我认为（a）在您的情况下，1/2英寸的间距将起作用，（b）您不必担心佛罗里达州的大雪。

   -- Martin Holladay

7. 
   彼得·L|2017年3月17日下午10:38|#7

   马丁，

   我实际上在西南沙漠（4b区）。

   1”的差距,也应该帮助和sound transfer from the metal roof, right?

   金属屋顶倾向于传递声音，而SIPS由于缺乏空气空间而可以传递声音。较大的1英寸差距会帮助声音传输吗？

8. GBA Editor
   马丁·霍拉迪（Martin Holladay）|Mar 18, 2017 05:18am|#8

   Peter,
   I'm sorry that I got your case confused with Jacob's. (That's always a risk when you piggyback on an existing thread.)

   您决定使用SIPS显然会增加赌注。我不熟悉您正在谈论的金属子礼物。这些金属子饰品是否允许拱脚式通风，或者仅从左到右通风（耙开通风）？

   -- Martin Holladay

9. 
   彼得·L|Mar 19, 2017 02:00am|#9

   马丁，

   It's mainly left to right venting (rake) since the sub-girts run from rake to rake.

   The metal roof is designed to install over roofs that don't have sheathing so the sub-girts raise the metal roof and the sub-girts allow the metal roof to clip into the sub-girt for retention.

   MBCI is the roofing company.

10. GBA Editor
    马丁·霍拉迪（Martin Holladay）|Mar 19, 2017 06:48am|#10

    Peter,
    sip屋顶使我感到紧张。我也听说会失败的故事。

    如果这是我的房子，我不会试图偷工减料。我要确保在sip上方有s脚到摩擦。

    -- Martin Holladay