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kittysmitty
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# Posted: 4 Mar 2019 09:37am
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In the process of building a small bunkie in the spring. Will be using 2x4 for roof rafters and cathedral ceiling. The 2x4 limits the amount of insulation so I'm thinking of doubling up the 2x4 to make them basically 2x8. Most are probably asking why use 2x4 in the first place. I do some work in construction and have a good source for used materials. First question how will this increase the strength of the 2x4? and second to you see any issues? Thanks
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snobdds
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# Posted: 4 Mar 2019 11:23am - Edited by: snobdds
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One thing I have learned over the years about utilizing used material is...it always ends up costing more in the end. It stems from having to do double work just to make the used stuff work, it is beyond frustrating. Plus, I would never build a rafter roof using 2x4, just not enough strength to hold up a roof. A 2x4 truss roof is a totally different and should not be considered equal.
I purchased some new windows from a lumber yard that were the wrong size for the original customer. I knew I would need them for my cabin build, but I was still 2 years out. I stored them in a corner of one of my rental houses garages until I needed them. I made sure to cover them and felt they would be ok. Two years later I loaded them and took them up to the cabin. Framed in the rough openings and finally took off the cardboard and plastic. Every single one of the window was warped and not square anymore. Every single window had to be trashed. I ended up having to order new windows.
I see the same thing here. It's not much more to just buy the proper roof rafter size and build off of that. It will always be stronger and you will never worry about it again.
My dad always told me to buy once, cry once and it's too expensive to be cheap. I wish I would have listened to him...
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kittysmitty
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# Posted: 4 Mar 2019 12:17pm
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snobdds
Thank you for your opinion.
Just a couple of points. I'm a firm believer in the 3 "R's". Reduce, Re Cycle and in this case Re Use. I have the 2x4's, it took some physical labour to remove and de-nail but will save a few trees being cut down in our forests.
Second point, The Canadian National Building code shows that 2x4 meet code requirements for my spacing, spans and snow load.
And last, sorry to hear about your window problem, but in my opinion there is a big difference in a piece of 2x4 lumber and a fabricated window.
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Brettny
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# Posted: 4 Mar 2019 04:03pm - Edited by: Brettny
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If you only want to add another 2x4 for the insulation depth stacking them should be fine. I do not think they will be as strong as a 2x8. If you want to make it stronger than a 2x4s and only have 2x4s i would use 3 2x4s. Two on end and one connecting them. All 3 standing on end.
Theres really no good way to connect 2 2x4s on end with out adding other lumber.
The real question is how long of a run will these 2x4s be and how much snow do you get?
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socceronly
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# Posted: 4 Mar 2019 04:16pm
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The discussion on keyed beams that was had recently might come into play here.
2 2x4 stacked would not equal a 2x8. Unless they are joined properly, according to that discussion, they would not offer any improvement over a single 2x4.
This might be a bit different as they are on an angle, but used as a beam it would not help.
Just get 2x8s.
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montecristo
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# Posted: 4 Mar 2019 04:21pm
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It's going to be more trouble than it's worth unless you make roof trusses with them. Just get 2x8's. There will be plenty of other projects to use the 2x4's on.
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Just
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# Posted: 4 Mar 2019 05:26pm
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If one 2x4 is strong enough and all you need is space for more insulation then cut some chipboard strips and scab two two by fours together you could leaves space between them for even more insulation.
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kittysmitty
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# Posted: 4 Mar 2019 06:22pm
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Yes, one 2x4 is strong enough, 6 foot span. Don't need extra strength, just more room for insulation. I like the idea of scabbing them together with chipboard or plywood. Thanks
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rockies
Member
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# Posted: 4 Mar 2019 07:33pm
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If you must use 2x4 (which typically are only 3 1/2" deep) then double them up side by side instead of stacking them to try and mimic a 2x8. At least then you won't have to scab them together.
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ICC
Member
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# Posted: 4 Mar 2019 09:38pm
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Quoting: kittysmitty The Canadian National Building code shows that 2x4 meet code requirements for my spacing, spans and snow load.
OK. So what type of ceiling is planned? T&G boards, sheet goods?
Will the insulation be spaced down from the roof sheathing to provide ventilation, or what?
If the Canadian code states the 2x4 have the strength for the span and snow load situation what amount of insulation is required for their energy conservation code?
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ICC
Member
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# Posted: 4 Mar 2019 09:39pm
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Quoting: rockies If you must use 2x4 (which typically are only 3 1/2" deep) then double them up side by side instead of stacking them to try and mimic a 2x8. At least then you won't have to scab them together.
That does nothing at all to address the OP question regarding increasing the amount of insulation.
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toyota_mdt_tech
Member
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# Posted: 4 Mar 2019 10:33pm - Edited by: toyota_mdt_tech
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Quoting: snobdds One thing I have learned over the years about utilizing used material is...it always ends up costing more in the end.
Well snobdds, looks like you didnt even make a dent. kitty didnt like your answer and is doing it anyway.
My dad said something about penny wise and pound foolish or tripping over a dollar to pick up a nickel.
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kittysmitty
Member
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# Posted: 5 Mar 2019 05:47am
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ICC
Not sure what ceiling yet, possibly 1/4 inch sheets of OSB, plywood, paneling or v joint pine paneling.
Yes insulation will be spaced down with soffit and ridge vents.
I was using the building code to make sure the 2x4's were strong enough. The building won't be inspected and i'm not concerned on what the code calls for insulation.
Building use will be limited to a few times a year and just for sleeping. It could be used in the winter, so that's why the insulation concern.
Thanks
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ICC
Member
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# Posted: 5 Mar 2019 10:29am
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Why not build a flat ceiling and simply toss the insulation on top of the ceiling just as so many homes are built? The attic space is easy to ventilate. If you are planning on a loft for sleeping those are usually brutal in almost any season; too hot when the lower level is good. ???
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rockies
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# Posted: 5 Mar 2019 07:34pm - Edited by: rockies
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ICC: Kitty probably wants to have a loft.
I agree that doubling up the rafters will do nothing to increase the amount of insulation but at 3 1/2" of depth you'll only have enough room for 2" of insulation (leaving you a 1 1/2" deep vent channel - which isn't really enough). With all the baffles, insulation, eave and ridge vents needed it's all a bit overkill for such a thin roof.
I suggest using an exterior insulation board. On top of the sheathing put a layer of 30 lb felt paper, then the rigid insulation board, sleepers, a 2nd layer of sheathing and then your roofing. The inside of the cabin roof can be left open or finished with a ceiling, but you won't have to worry about vents, air channels or moisture buildup in the roof cavities.
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Just
Member
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# Posted: 5 Mar 2019 08:02pm
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R40 batt insulation 4 in. Ventilation cavity,works for me .
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kittysmitty
Member
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# Posted: 6 Mar 2019 06:46pm
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ICC
No Loft and have decided to go with flat ceiling, makes more sense. Besides with a cathedral ceiling, just more space to heat. Thanks Everyone .
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