Framing Questions for a Tiny House

BostonMan · October 16, 2012, 10:53:05 AM

Hello -
First post on this forum, have really enjoyed reading about everybody's project! I'm planning on building a Tiny House on a trailer this upcoming spring and have some questions about the framing of it. Since it will only by 8' x 17' I am hoping to minimize weight/maximize size by scaling down the framing:

1 - Planning on using 2x4's for the floor and wall framing. Do you think I can get away with using 2x4's for the roof and loft framing? Maybe if they're 16 O.C?

2 - Wondering if anyone had some advice/photos on framing out the loft joists. It will only be half the house, 8' x ~8'. Can I use 2x4s? Maybe 4x4s? I don't want to lose those 2" in the ceiling that a 2x6 would take away. Also is it necessary to put a cripple stud under each loft joist, or would attaching them to the studs be sufficient, with bolts?

3 - What is the "flattest" pitch of roof that I could get away with, the building can only be 13.5' (including the tires and trailer) and I want to be able to maximize the wall height.

Thanks a lot.

MountainDon · October 16, 2012, 08:29:16 PM

Quote1 - ... using 2x4's for the floor and wall framing.

Walls; no problem except maybe for the amount of insulation you can place in there.
Floor; Even placing floor joists on 12 inch centers, and reducing the average floor load to 30 PSF instead of the usual 40 PSF, 2x4's in the commonly used species and common grade #2 don't quite make the grade. They fall short by 6 to 10 inches. Select Structural grade comes closer, within 2 inches for Southern Pine and Doug Fir in Select structural. That might not be easy to find. If you keep the floor loads light you could probably get away with great 2x4's.

Quote2 - Wondering if anyone had some advice/photos on framing out the loft joists

Considering that a true loft may just have a mattress and some blankets you can get away with std #2 2x4 for the loft floor, IMO.

Quote3 - What is the "flattest" pitch of roof that I could get away with

Depends on the roofing. Shingles are normally limited to a minimum of 4/12 pitch. If you were to sheet the entire roof deck with ice and water shield with shingles over that, you can go lower.

Are you thinking of a shed roof or a gable roof? (shed has one wall higher than the other whereas gable has a higher ridge down the center with walls at a lower height. With a gable roof, the lower the pitch the greater the outward horizontal force. IMO, with an overall total height limit of 13'6" and an 8 foot width it will be difficult to achieve a useful loft height and still have standing room below.

October 17, 2012, 08:40:35 AM

Wow, thanks a lot.

Yes, the loft will only have a mattress. I'm thinking of maybe using 4x4's 24" OC so I don't lose the 2" that I would with 2x6 but keep the same structural integrity. Could I possibly do the same for the roof joists?

Roof - It will be a gable roof. I've attached a picture of a quick drawing I've done in sketchup of what the loft might look like. There will be around 3.5' in the loft. A little tight but if it's just for sleeping that should be sufficient. Using 2x4s does help quite a bit, I put the 2x4's on one side and the 2x6's on the other to compare the 2. I could always drop the walls a couple of inches.

(Not totally sure how to add photos on here)

MountainDon · October 17, 2012, 09:04:30 AM

http://countryplans.com/smf/index.php?topic=11663.0

BostonMan · October 17, 2012, 09:53:42 AM

These are two shots of the loft with a queen size bed in it. Thanks for that info, had to sign up for photobucket but they make it really easy to copy and paste, very cool.

October 17, 2012, 11:42:04 AM

A gable roof spanning 8 feet total, 4 feet per side should present no problems with 2x4's.

As illustrated the loft floor / ceiling joists act on the top of the wall as rafter ties, making the roof / walls there quite sturdy. If the loft floor joists were dropped down the wall some of that disappears.

You should have rafter ties, maybe as beams, across the width at the other end as well/ Without rafter ties the load on the rafters will cause horizontal outward forces to spread the wall tops. With a low pitch roof these outward forces can become greater than the downward forces. The connection of the rafters to the rafter ties and to the wall tops becomes very important.

BostonMan · October 17, 2012, 12:16:22 PM

Thanks a lot MountainDon, I've been seeking out a logical answer to this question for a long time. Also I really appreciate your posts, are you the same MtnDon on small cabin forums? Also really appreciate that site as well

MushCreek · October 17, 2012, 04:48:58 PM

Since I assume you are sheathing it with sheet goods, such as plywood or OSB, 17' long would be very wasteful. 16' would be ideal, or 18' (half sheet width).

firefox · October 17, 2012, 09:34:38 PM

Unless esthetics is a driving force her, I would think that a flat roof would be ideal
for something that is only 8 feet wide. This would allow you to use 2x6's and still have room to spare. It would make the loft far more comfortable and you would even
have space for small closets for pj's and linen.
You could use tapered foam on the top for a small slope just so water doesn't puddle. Then use a thick membrane over that. Yes, I know it is not glamorous,
but after you live in this for a few months, you will thank me.
Bruce

October 19, 2012, 03:58:00 PM

I I know that 17' is not an ideal length but I'm letting the trailer dictate the size and when the house is so small that extra 8 sq. ft. is hard to pass up. I'm thinking of doing a 6" overhang on the front and back of the gable end which would make the roof 18' long. For the walls I'm considering using LP smartside lap siding because I have read and seen that you don't need to add sheathing, has anyone here used this product?

I was considering a shed roof but I do think that I would just prefer a gable. I might add a dormer to one of the side to give the loft a little extra space.