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Just getting started, first question about insulation

MattieTwo | Posted in General Questions on

I rediscovered this website/forum last night when looking for a solution to a shower question and found a question here about a similar situation. I needed to be registered in order to search for that poster to see if he ever found a solution and found that I was already registered. Apparently I registered a few years ago, maybe when I needed to search for a solution for something then too. The poster either never found a solution to his problem, or didn’t post about it if he did, but I started reading some of the posts that did come up in my search and was surprised to see how similar our goals for our new build are with the green building goals. We have built traditional homes before, but we are in new territory now and have a lot of questions with few people to ask.

Background: We are building a barn home – a weld-up metal building. I know these are not popular here, but we chose this method of several reasons. Only time will tell if it is the right choice. We are in hot, humid, Texas.

Our building is a rectangle, set near the top of a rise (not really a hill, but not flat land either). Very little wind breaks; spring and fall are very windy. The long sides face north and south and have most of the windows. All but two south windows and all but one north windows are under 10 foot porches. The windows under porch also have shutters which can be closed to protect them and the interior space. There are two windows on the west side which also have shutters, and there are two windows on the east side which have no over hang and no shutters, but facing east, there shouldn’t be a problem with them.

Next to the living space is a drive through garage which will have screens so it can double as outdoor living/breezeway and will also have a mini kitchen to reduce cooking heat in the living space in the summer. The stairs are in the center of the living space with a cupola above it to pull heat out and hopefully reduce the need for as much air-conditioning. Air-conditioning is a big concern, but it’s not immediate so I’ll come back to that later.

The plan is to spray closed cell foam the inside of the entire metal building, 1 inch. The living space will be built with 2×4’s inside the metal building faced with solid foam core and set 2″ apart from the metal framework. We’ll use batt insulation between the 2×4 exterior walls and between first and second floor. Then sheetrock on walls, beadboard ceilings, hollowcore interior doors, insulated steel exterior doors. Windows are vinyl clad aluminum.

We have received so much conflicting information about insulation, mainly from the people giving us bids. And reading here, I see there is also a difference of opinions. Builder of the metal shell said use 1-1/2 inch of closed cell because it is waterproof and will insulate better than 3 inches of open cell. Insulation company #1 says use 1 inch of closed and 3 inches of open on top of it to give better Rvalue and to make the walls have less flex and so less noise when the wind blows. Company #2 says no, use only closed cell and do 2 inches and it will have the same R value as the combination of closed and open. These are people who have never done the wood framing separated from the metal framing. The usual way these barn homes are built is to attach the studs directly to the metal. We aren’t doing that for 2 reasons: 1) temperature transfer 2) sheetrock damage due to metal expanding and contracting.

Because we are insulating the wood structure well, and because there is an air space between the insulated metal building and the insulated wood building, husband doesn’t feel that the metal part needs more than 1 inch to seal all the openings (and there are many) and make it watertight.

We have company #3 scheduled to spray in 10 days, so we have plenty of time to second guess our decision. What are your thoughts on this?

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  1. GBA Editor
    Martin Holladay | | #1

    1. If you leave 2 inches between the metal frame and the 2x4s, with the 2 inch gap be insulated or uninsulated?

    2. What is your plan for the ceiling above the top floor -- also 2x4s filled with fiberglass, or something more substantial?

    -- Martin Holladay

  2. GBA Editor
    Martin Holladay | | #2

    One more question: Can you describe what the inside of the metal building looks like -- the surfaces that will be sprayed with foam insulation? I assume that the interior has exposed steel posts (columns), exposed steel beams and girts, and (on the exterior side of these posts and beams) some type of steel cladding. Is this correct?

    In other words, does it look something like the buildings in the photos below?


  3. MattieTwo | | #3

    Martin, I'll answer your questions as best I can, but my terminology may not be right.
    1. As I understand it, the airspace won't have anything in it and will just be to keep the wood from contacting the metal. It may not be a full 2 inches depending on if a scrap of 2x4 is used for a spacer. One barn home we visited during its construction had 5/8 inch air space and had used metal brackets to attach the wood framing to the metal framing every 10 feet top and bottom. I don't know if that is the plan for ours. It will be attached at all the windows and doors so will have to be attached in places with something, I'm just not sure what.

    2. The plan for the ceiling, I think, is 2 inches of foam on the metal above the living area, and insulation in the wood framing. Whether that is 2x4, I don't know.

    3. Yes, the inside of our building looks a lot like your photos. Red metal. The columns are larger and just two girts that look further apart than those pictured. No trusses like those pictured though, it's all open. I don't have any pictures of ours inside but will see if I can find one online like ours is made.

  4. MattieTwo | | #4

    How do I add an image I found online?

  5. GBA Editor
    Martin Holladay | | #5

    To add an image, click the option called "File attachments" under the comment box. Options will appear; click the "Browse" box, and then select a photo that you have saved to your computer's hard drive or to your Desktop. Once you have selected the correct image, click "Attach," and then "Post."

    -- Martin Holladay

  6. GBA Editor
    Martin Holladay | | #6

    If you want to use fiberglass batts as insulation between 2x4 studs, you need air barriers on both sides of the studs.

    It would really be better to fill the air space between the studs and the cured spray foam with some type of insulation, rather than to leave an air space. The air space leaves opportunities for convective loops and hidden air leakage paths.

    -- Martin Holladay

  7. MattieTwo | | #7

    I showed my husband this discussion as well as information I found on convective loops and double wall construction. He has been researching the insulation side more than I have and his brother used to be in the metal building insulation business - here is what he said, but in simple language. Since the metal wall will be insulated as well as the stud wall, it won't be a big temperature difference between the two. We both wonder if it would make a big difference to fill the entire void between metal, but cost is a factor right now and we're stretching it to put 1 inch over the whole building.

    The 2 inch air gap will actually be more like 3/4-1 inch when finished but it is necessary to have an airspace for foil faced rigid insulation. Using a 2x4 spacer between the metal and wood framing makes the air space 1-1/2 inch, and the rigid insulation will be on the air space side of the framing. Batt insulation will be between the studs, and sheetrock on the living space side of the studs.

    Everything we have read and been told by people who have built these is that the wood should not be against the metal. Those who built them with the air space say they work really well. Those who put the wood against the metal say it was fine at first, but a few years into it they started having problems with the building sweating and sheetrock cracks.

    I forgot to ask if our upper floor ceiling is going to be 2x4 or something else.

  8. GBA Editor
    Martin Holladay | | #8

    It wasn't clear to me (from reading your first post) that you planned to install foil-faced rigid insulation between the cured spray foam and the 2x4 framing. That layer (the foil-faced rigid foam insulation) will definitely improve the performance of the wall assembly compared to a wall assembly without the foil-faced rigid foam.

    Since your husband appears to know more about these details than you do, here's what I'm wondering: Does your husband have any questions? If so, perhaps your husband should post them. Otherwise, it feels a little bit like we are playing telephone.

    -- Martin Holladay

  9. MattieTwo | | #9

    Yes, it would be nice if he would post. So I guess I'll let this drop because he isn't going to do it.

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