Hi,
I am renovating an old log house and will soon be making a new attic floor structure. The attic will be an unheated space and will only be used for access and inspection. I will not lay any flooring in the attic, but the floor structure will be insulated, and there will be paneling on the underside. The dimensions of the attic floor structure will be 7x7.2 m.
Since it will have such large spans, I am unsure how to construct the floor.
Option 1
Frame without load-bearing beams using 45x220 C24 7 m finger-jointed or use shorter in the same dimension which I splice with screw-glued overlap. By far the cheapest, but I guess it will be too much deflection with that span even if the attic is not used.
Option 2
Two laminated beams and place floor joists in between. The best option but I don't know which dimension I need. The calculation tools available online are based on a completely different load and deflection requirements. Moreover, few suppliers stock laminated beams over 7 m, and I would need to get hold of it fairly immediately.
Option 3
Splice two laminated beams into one load-bearing beam. Buy, for example, 66x315 6 m which I lay side by side to make 7 m, i.e., 5 m overlap in the middle and patch in the last meter at each end in the same dimension. To reinforce it further and have something to lay the floor joists on, I lay a 45x195 lying in the bottom and possibly on the top. Everything is screw-glued.
If anyone has any good tips, they are gratefully received!
I am renovating an old log house and will soon be making a new attic floor structure. The attic will be an unheated space and will only be used for access and inspection. I will not lay any flooring in the attic, but the floor structure will be insulated, and there will be paneling on the underside. The dimensions of the attic floor structure will be 7x7.2 m.
Since it will have such large spans, I am unsure how to construct the floor.
Option 1
Frame without load-bearing beams using 45x220 C24 7 m finger-jointed or use shorter in the same dimension which I splice with screw-glued overlap. By far the cheapest, but I guess it will be too much deflection with that span even if the attic is not used.
Option 2
Two laminated beams and place floor joists in between. The best option but I don't know which dimension I need. The calculation tools available online are based on a completely different load and deflection requirements. Moreover, few suppliers stock laminated beams over 7 m, and I would need to get hold of it fairly immediately.
Option 3
Splice two laminated beams into one load-bearing beam. Buy, for example, 66x315 6 m which I lay side by side to make 7 m, i.e., 5 m overlap in the middle and patch in the last meter at each end in the same dimension. To reinforce it further and have something to lay the floor joists on, I lay a 45x195 lying in the bottom and possibly on the top. Everything is screw-glued.
If anyone has any good tips, they are gratefully received!
I think it is realistic to anticipate a widespread load of 1 kN/sqm including self-weight. Alternative 1 does not work. The deflection becomes far too large. I would like to propose another option. Use only glulam beams but place them at c/c 1200 mm. Insert nail battens between the glulam beams for the ceiling. Alternative 3 can probably work, but it is unsightly and bulky.
A suitable dimension for glulam according to my suggestion is 90x315.
A suitable dimension for glulam according to my suggestion is 90x315.
Thank you for your response!
It's a good idea, but is it possible to do it more cheaply? If I manage to get 5 pieces of 90x315 9 m support beams, it costs about 17k. My idea is that the load-bearing structure should not be visible from below. Is glulam a reasonable alternative? Would it, for example, work to place two pieces of 45x450 and put 45x195 cc 600 in between? The price for the glulam beams is 5600.- for two 8 meters.
Are there any good collections of formulas online so one can do some calculations themselves?
It's a good idea, but is it possible to do it more cheaply? If I manage to get 5 pieces of 90x315 9 m support beams, it costs about 17k. My idea is that the load-bearing structure should not be visible from below. Is glulam a reasonable alternative? Would it, for example, work to place two pieces of 45x450 and put 45x195 cc 600 in between? The price for the glulam beams is 5600.- for two 8 meters.
Are there any good collections of formulas online so one can do some calculations themselves?
Veneer and masonite beams are all interesting options, but not in combination with regular construction timber. A laminated beam along the ridge direction in the middle combined with regular construction timber fitted with joist hangers can be an option. The support beam should in that case be 90x405 and the joists 45x170.
What we are working on now, structural system design, lacks good resources online.
What we are working on now, structural system design, lacks good resources online.
Out of pure curiosity, why don't we combine veneer beams with construction lumber?
A longitudinal beam might be an option if I can set up posts that support it properly. How much bearing does that beam require?
Another thing I've been thinking about is if I screw-glue a joist lying on the underside of a glulam beam to create a support for floor joists. How much do the screws affect the beam's load-bearing capacity? A certain amount of wood fibers are torn apart by the screws where the greatest load is, but maybe it's negligible.
Very grateful for the help!
A longitudinal beam might be an option if I can set up posts that support it properly. How much bearing does that beam require?
Another thing I've been thinking about is if I screw-glue a joist lying on the underside of a glulam beam to create a support for floor joists. How much do the screws affect the beam's load-bearing capacity? A certain amount of wood fibers are torn apart by the screws where the greatest load is, but maybe it's negligible.
Very grateful for the help!
There is nothing to say that you can't mix and match wildly between veneer beams, glulam, and kerto. Glulam is often chosen over veneer if it will be visible.
As you are certain, the damage from the screws is negligible, it actually becomes a reinforcement with the additional rule you screw in. It's quite a substantial load-bearing construction you're taking on, so make sure to get it dimensioned. Moelven has an online service you can use, and the Wood Guide has many dimensioning tables.
As you are certain, the damage from the screws is negligible, it actually becomes a reinforcement with the additional rule you screw in. It's quite a substantial load-bearing construction you're taking on, so make sure to get it dimensioned. Moelven has an online service you can use, and the Wood Guide has many dimensioning tables.
Nothing is set in stone, but my perception is that masonite beams and veneer beams are not intended for lateral fastenings, in order to keep the construction's height down.
Unfortunately, it seems that Moelven has discontinued the glulam app, which I found to be very good, and the beam program on the website requires login and appears to be aimed at industry professionals. A problem with the tables and guides from the wood guide is that they often assume the same load, typically 2kN/m2 if I remember correctly. I calculated the floor structure's own weight some time ago and recall it was around 0.4kN/m2 excluding any girders. Then there's my 75kg as a point load when I crawl around and inspect the attic. I understand that there is a good reason why tables and programs for private individuals are very simple, but it leaves me wanting more, and it would be fun to delve deeper into the subject without having to study engineering.
Regarding lateral fastening on a laminated beam, that's exactly what you see in the picture at Beijer when you go into the laminated beam category. By that, I don't mean that it's right or wrong, but that's what the picture shows, alternatively a horizontal beam at the bottom, which I was considering.
The fundamental strength of materials and building mechanics is not particularly difficult. At the same time, everything around it has become more complicated. No one dares to publish anything that is not correct in every situation. Does the problem sound familiar? All types of light beams exploit the fact that a beam's stiffness primarily increases with its height. A solid beam is, in my opinion, superior when it comes to possibilities for fastenings.
Yes, masonite beams don't handle large loads in attachments; that's true. It's possible to calculate but not common. Veneer beams are very strong when it comes to attachments. In the standard, they are handled in exactly the same way as glulam and studs, just with slightly different material parameters regarding the dimensions.J justusandersson said:
Yes, spontaneously it feels like the Limträappen was withdrawn to cover themselves so that an accident cannot be attributed to the app being misinterpreted or used incorrectly. Regarding fastening in veneer beams, screwing from the side across the boards should be reasonably equivalent to solid wood, right? However, I imagine that screwing from underneath along the glue line is not the same thing.
The reason the tables start with the same load is that it is standard regulated. You don’t actually have the freedom to design according to the load you will specifically cause. For attics, I don’t have the standard requirements in mind, but I believe it is between 50-100 kg per square meter depending on the free height. Even if there’s not a floor, the next owner might lay down some planks and pile up boxes. It’s not uncommon at all.Z Zoidberg said: