I am using Sketchup and planning to model our proposed guest house in the countryside in Roslagen. I made a similar model a few years ago when we built a patio, and it worked very well.
It will be a 25 sqm Attefall house with a gable roof, two rooms, and a sleeping loft. No sanitary facilities, those will be in the main house.
I plan to use the model as a basis for getting proposals from construction companies.
But it would be good to use the "right" dimensions for the studs and such, of course. The house will be 3.7x6.45 externally, and we thought 15 cm would suffice for the wall thickness.
There should be insulation, of course, but not for arctic winter, we only stay out there during the summer half of the year...
What I would like to know is what dimensions are normally used for:
- The framework in the exterior walls with 60 cm spacing on the standing studs (45x70, 45x95, or 45x120)
- Sills in the floor construction with 3 longitudinal sills (45x170, 45x195, or 45x220)
- Cross beams in the floor, span about 1.8m in joist hangers on the sills (45x145, 45x170, or 45x195)
The roof must be open inside (no ceiling or attic), so we thought to use a laminated beam as a ridge beam supported in the gables and the partition wall between the two rooms. The span will be about 3.7 + 2.7 m for the two parts.
Then, instead of rafters, we thought of installing roof joists between the beam and the tops of the walls.
Should we maybe have two rafters (one in each gable) and then load-bearing posts in the partition wall?
What dimension seems suitable for:
- The laminated beam in the ridge
- The roof joists
Grateful for all the tips.
PS: Is there a website with dimensioning help for these kinds of questions? DS
In the wall, you should have at least 45*95, but if you want more insulation, choose larger.
The sill will be as wide as the wall studs.
The floor must be at least 45*120 C18, but I recommend larger because cold floors are not fun.
Regarding the roof, I have calculated snow zone 2 and concrete tiles with insulation and interior lining.
If you have such a roof, the following dimensions are required:
Pillars in exterior walls: 120*45 C14
Pillars in the middle: 90*90 GL28 h construction timber
Wood beam at the ridge: 220*45 C24
Roof rafters: 45*120 C14
I found a building description for a prefab cabin in Allt om Fritidshus nr 4 2013 (pages 56-57). Unfortunately, there doesn't seem to be an online version of this magazine's articles so I can't link...
They haven't provided main measurements for the cabin, but it looks like something along the lines of 3.5x4.3m, possibly longer and narrower.
However, they have provided lumber dimensions:
- support beams and rafters in the floor 45x170
- walls 45x95
- roof beam (ridge) 2 glued together 45x220
- support pillar for roof beam 90x95 (2 glued together 45x95)
- roof joists with a spacing of 600 mm 45x170 <= quite thick I think. Isn't 120 enough?
In my case, the frame width will be 3628 mm, meaning the roof joists should span 1814 mm sideways with a 25-degree slope. Shouldn't 45x120 be enough, or will that leave too little room for insulation?
I just measured the roof of the existing cabin (Västkuststugan) and the trusses here are built with 120 mm high lumber even though the span is 5 m, meaning each leg spans 2.5 m.
So 120 should be enough for my Attefall build too, right??
That's what you're suggesting, but what does C14 mean?
If you use this kind of profiled metal roofing (looks like roof tiles), it will be lighter and thereby even safer with 45x120, right?
These dimensioning links lead to pages where you need to log in and provide a name, etc., and I'm not too keen on that, as I already get enough spam emails...
Dimensioning is tricky, but I don't want to optimize for low cost; I just want to use something that will work according to "rule of thumb"...
At the same time, I don't want to waste on height measurements because it's important to stay under 4m from the ground at most.
I found a construction description for a "friggebod" in Allt om Fritidshus no. 4 2013 (pages 56-57).
Unfortunately, there doesn't seem to be any web version of this magazine's articles, so I can't link to it...
They haven't provided the main dimensions for the cottage, but it looks like something in the style of 3.5x4.3m, possibly longer and narrower.
They have specified the timber dimensions anyway:
- floor joists and beams 45x170
- walls 45x95
- ridge beam (peak) 2 glued together 45x220
- support pillars for the ridge beam 90x95 (2 glued together 45x95)
- roof rafters with spacing 600 mm 45x170 <= pretty thick, I think. Isn't 120 sufficient?
In my case, the width of the frame will be 3628 mm, i.e., the roof rafters should span 1814 mm in width with a 25-degree slope. It should work with 45x120, or will there be too little space for insulation then?
I just measured the roof of the existing cottage (Västkuststugan), and the trusses here are built with 120 mm high timber, even though the span is 5 m, i.e., each leg spans 2.5 m.
So, wouldn't 120 be enough for my Attefall construction too??
That's what you're suggesting, but what does C14 mean?
If you use this profiled sheet metal (looks like roof tiles) as cladding on the roof, it will be lighter and thus even safer with 45x 120, right?
These dimensioning links lead to pages where you have to log in and provide names, etc., and I'm not too keen on doing that, I already get enough spam emails....
Dimensioning is difficult, but I don't want to optimize for low cost, just choose something that according to "rules of thumb" will work...
At the same time, I don't want to waste the height measurements since it's about staying below 4m from the ground at most.
Some quick thoughts and responses from my side:
C14, C24, etc., are strength grading of the timber. A higher number indicates higher strength. They are usually stamped on them. At Byggmax, it's typically C14 studs, whereas more well-assorted building suppliers often have both C14 and C24, sometimes even higher classifications.
25 degrees seems to be an unusual slope; normally, you start from "even parts," i.e., 14 degrees (1:4), 18 degrees (1:3), 22 degrees (1:2.5), 27 degrees (1:2), etc.
Of course, there's nothing stopping you from having exactly 25 degrees if you want.
I think you should use 145mm studs as roof rafters, if for no other reason than for the insulation, keeping in mind that you will lose some space for ventilation. I believe it's necessary if you want a heavy roof as well (tiles or concrete tiles).
Since you have a central support for your ridge beam, you don't need to use glued laminated timber, a regular 220mm high stud works fine.
Another thing to consider is that you save minimal money by skimping on the framing. This is an insignificantly small part of the cost of the entire house anyway, especially if you outsource the work.
That's what I meant with my comment about the sizing.
Money is not a problem, but it should be durable while not wasting too much vertical space, as I also need a sleeping loft within 4m...
I would have opted to skip the pillar in the middle if possible; if you want to change the floor plan in the future, it's nice not to have to worry about a pillar in the middle of the cabin. In my "friggebod," I used a 90x315 glulam beam; it protrudes a bit below the roof joists, but I find that just looks nice. I think it has a span of slightly over 5 meters...
Thanks for the link to your project!
I've also been thinking about how to handle the TV mounting...
Your solution looks clever!
However, there is no problem with the roof ridge layout. I place a post at each gable and one in the partition wall roughly in the middle of the house. Only one half has full ceiling height, the bedroom will have a ceiling and above it will be a sleeping loft for the kids. Entrance to the loft on one side so there will be full partition wall height where the post is placed (two glued 45x95 beams).
I'm continuing to work on my model in Sketchup...
I've now replaced the roof beams with 45x145 so that more insulation can fit.
Additionally, I've spaced them out so there's a "truss" on every other standing stud in the wall, seemed overkill to have roof beams every 600 mm.
I'm working towards a total height of 4000 mm so now I'd like to know how much the roof covering adds to the ridge height calculated from the finished tongue and groove roof?
Does anyone have a rule of thumb for this?
With this measure, I can lower the roof just as much as needed and then I'll see how the loft space turns out...
I will have a sleeping loft above the bedroom at one end of the house. So I'm wondering how to size the floor in the sleeping loft?
The interior dimensions of the house are 6440x3390mm and the bedroom will be 2700x3390 mm with a ceiling height of 2100 mm.
So I guess I need to place the beams along the house from the top of the partition wall to the gable wall?
Is 45x120 or maybe even 45x95 enough for these if I place them with 600 mm spacing? They only span 2.7m and there will be 22mm flooring chipboard on top and an OSB board underneath.
And how do you attach the beams to the gable wall?
Can you screw a ledger horizontally on the wall directly into the studs on the "other side" of the wallboard (OSB)?
That would be the simplest, and you could remove the floor later if you want to remodel the whole thing...
Do you understand what I mean without a picture?
I could "sketch up" what I'm thinking and show it...
Found the following help page online where you can size roofs, floors, etc.: Byggbeskrivningar-dimensionering
Got some options for the roof and the floor of the sleeping loft.
Reporting to help any potential readers who found this thread through searches.
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