Truss question for Garden Shed Build

[GPintheMitten]

P.S. With rafters and floor joists, you can more easily create an opening in the floor where you need/want it. Just use doubled headers and doubled joists, sort of how you would for a window opening in a wall.

Also, if you make a door for the attic in the gable on the outside of the back of the shed, you can get access via a ladder from the outside. You could make a door on both gables if you want.

 

[GPintheMitten]

Personally for the ridge board I would use a 2x not a 1x, just makes it stiffer during construction. Because the 2x8 rafters are cut on the angle for the roof pitch, they will be longer than 7 1/4 inches, so I would go with a 2x10 ridge board.

 

[rtimgray]

I'm in the stick-building camp as well, and you can overbuild or underbuild as much as you wish. 2x10's would be great for the floor joists, but probably aren't necessary, since it's not going to be walked on a lot. Same with rafters - 2x8's would be great, but each rafter run is probably going to be less than 10', so 2x6 would be plenty. I bet you could build it either way and it won't fall down.

Good luck and take care.

 

[GPintheMitten]

I recommend you check some span tables. I'm no expert, and I could misread them but here's what I found on Span Tables :: Southern Pine . It looks like they are charging for downloads now but I downloaded a couple of tables about a year ago.

For Floor Joists with a 30 Pounds per sq ft (psf) live load of 30, and 10 psf dead load, and 360 deflection, you could use a No.2 2x8's, 12 o.c to span 15' 7". Or you could use No.2 2x10's, 16" o.c. to span up to 18'. In fact they say you could span 16'5", 19.2" o.c., but I have never used 19.2" o.c. on anything. So, I would use No.2 2x10's on 16" centers.

I also checked the rafter table, for 50 psf live load, and 10 psf dead load, with 240 deflection. According to my reading of their table, you could use No.2 2x6's to span 8' 4" at 24" o.c. Of course, that means you could center them at 16" o.c. if you wanted.

When you are determining your span, you use the horizontal distance inside to inside, not the actual length of the rafter. So, assuming you are stick building the walls with 2x4's, the rafter spans 8'-(3/4" + 3.5") = 7' 7 1/4". Your floor joists span 16' - 7" = 15'3".

As for floor sheathing in the attic, I guess you could go lighter than 3/4", it depends on how stiff you want it and how you are going to load it. Roof sheeting for 16" o.c. rafters could be 1/2" osb.

 

[hunterridgefarm]

I recommend you check some span tables. I'm no expert, and I could misread them but here's what I found on Span Tables :: Southern Pine . It looks like they are charging for downloads now but I downloaded a couple of tables about a year ago.

For Floor Joists with a 30 Pounds per sq ft (psf) live load of 30, and 10 psf dead load, and 360 deflection, you could use a No.2 2x8's, 12 o.c to span 15' 7". Or you could use No.2 2x10's, 16" o.c. to span up to 18'. In fact they say you could span 16'5", 19.2" o.c., but I have never used 19.2" o.c. on anything. So, I would use No.2 2x10's on 16" centers.

I also checked the rafter table, for 50 psf live load, and 10 psf dead load, with 240 deflection. According to my reading of their table, you could use No.2 2x6's to span 8' 4" at 24" o.c. Of course, that means you could center them at 16" o.c. if you wanted.

When you are determining your span, you use the horizontal distance inside to inside, not the actual length of the rafter. So, assuming you are stick building the walls with 2x4's, the rafter spans 8'-(3/4" + 3.5") = 7' 7 1/4". Your floor joists span 16' - 7" = 15'3".

As for floor sheathing in the attic, I guess you could go lighter than 3/4", it depends on how stiff you want it and how you are going to load it. Roof sheeting for 16" o.c. rafters could be 1/2" osb.

Good information, thanks.

My plan for the ridge board is a 2x8 with 2x6x10 rafters spaced 16" OC if I go close to the 6/12 pitch this should give me a foot + hangover. Not enough room to stand up on the "second floor" but it is really not going to be a second floor but I plan to use 2x10's for the span or 2x12.

I did get the floor down last night and plan to go get 2x4's for the wall framing this afternoon or Saturday. I am trying to decide on a couple of windows. Also I plan to use some 100 year old french entry doors off of the old farmhouse we have. But may need to waite till cooler weather to remove those. I hope to get by the other farm where the house is to measure the doors so I can go ahead and frame the rough opening for them.

The doors are unique as one side has a full size door and the other is 1/2 to 3/4 the size of a regular door.

 

[GLyford]

and 360 deflection

Just remember the L/360 deflection is used for finished ceilings to keep the drywall and mud from cracking. It's far, far beyond the strength rating. So you can go for more deflection (springier floor) up to L/240 and still be well within the overall strength rating of the span for an unfinished ceiling.

 

[GPintheMitten]

Those French doors sound cool. Enjoy your project.

 

[GPintheMitten]

Just remember the L/360 deflection is used for finished ceilings to keep the drywall and mud from cracking. It's far, far beyond the strength rating. So you can go for more deflection (springier floor) up to L/240 and still be well within the overall strength rating of the span for an unfinished ceiling.

Good to know. I haven't studied the deflection attributes.

 

[SPIKER]

MOST of the suggestions here are going pretty much overkill for a "Garden Shed" type out building. I have 3 on my place most built LONG before I bought it. they all appear to have been built "On-Site" one with the pre-fab truss/hoop type design and is the most used but also just had to have the roof re-done. it is all 2x4 construction is 12' or 14'wide 20' long just as you described with part 2nd story in both ends and maybe 6~8feet open in center.

It used 1x pine sheathing boards (8"~10" wide I think) for roof & sides 2x4 wall & sills 24" OC roof hoops/truss (Gambrel) with the metal plates tying them at the joints. The 2nd floor boards are also 2x4 and on same 24" w 1/2 plywood (not OSB) exterior grade. I have owned it 12 years, the shingles (replaced 2 weeks ago) were totally shot looked like 25yrs old or more. NO SAG in this one anywhere. It also uses 2x6T&G treated floor boards setting on 4x4 or 4x6 running across it. (Looking at moving this shed soon as it is pretty much not where I would like it and would be an easy move. it sets on the END of my drive right next to the cabin. looking at moving it next to the 2nd shed below.

2nd Shed is 16/18' X 20/21' (see it here shed raise pictures by WPSPIKER - Photobucket )
My camera died when doing the job but a few good pics still made it in the link above.
wow did that 6 years ago seems like yesterday.

It was setting on coffee cans for foundation that were filled w quick crete (Seen in the PIC above) & dirt floor so was not as good of shape and probably the newest on the property.
It is same 2nd story FULL FLOOR about 4' high in 2nd floor so no walking. it also uses 2x4 on 24" stick built using the ridge beam 1x6 and fabricated side wall & roof all 2x4. Snow Load is much higher than you will ever expect down there same w weather changes & humidity. The 2nd floor 2x4s are sagging in it, MOSTLY due to the dirt floor in it for 10+ years. There are a couple vertical center dividers tying the roof ridge beam to the 2nd floor probably as much for roof support as for floor support. the 2 vertical supports have 0 sag in the floor 2x4 as the ridge beam helped support it. it only has 3/8" plywood and again light storage I been up there a few time it does have glass canning jars at end or against the roof/wall pitch and maybe 400lbs of misc lawn stuff up there. With the concrete floor I put in few years back it appears to have stayed same amount of sag (not gotten worse) just visual inspection. also was put together on the cheap uses the Hardi-Plank stuff for 4' wide doors (Really pretty good stuff) and 3/8 or 7/16 OSB for roof & sidewall sheeting.

3rd shed has built up on pier floor (Ground hog under it ruined this floor) side walls are made using old skids same with roof joist w metal on top. it uses the hardy siding which is very good. no leaks but the woodchuck has ruined floor and is all dirt under a wood floor joist system so wet moisture is the issue here. like the 2nd shed was looking at raising and concreting floor under it. I hardly use it it does have 1/2 2nd floor w 2x6 ~12 or 14' wide there even w moisture in it has no real sag but also nothing there for storage weight. some ole misc stuff is it the old guy used it for a wood work shop so just mist stuff.


Mark

 

[Cobble]

Ridge board and rafters - no question. Having gone both ways with small garages, I think the ridge board and stick build would be easier when working alone than trusses. All you need to do is erect a temporary vertical post on each end to locate the ridge board and then you only have to handle one rafter at a time.

+3 on Kenny G's suggestion.

I would frame up a "hole" in the storage space floor/ceiling to allow use of a fold down staircase for access to above. 16x16 will leave not room for stairs.