Hidden beam, HELP Urgent

[Gugge Grön]

I will be expanding the summer cottage in 3 weeks and will be tearing down part of an outer wall. During this demolition, an extension will be built with trusses in the opposite direction. The old trusses need to be supported. I do not want a support beam hanging down in the room below but want the ceiling to go unbroken throughout the room. I have considered many solutions and am attaching a document with three conceptual solutions.

Option 1: Using a truss as support, I am worried about how the attachment can be strong enough. I fear that the support beam will split open when there are large forces perpendicular to the grain direction.

Option 2 with Glulam requires some adaptations at the support points that weaken the beam. It requires a fairly high beam, about 450 mm. Even in this case, the attachment is the problem when you hang the supported trusses from the bottom of the Glulam beam.

Option 3. Using a U- or I-beam will probably require adaptations at the beam ends with cutting and welding work, which becomes expensive.

Does anyone have any tips? Is there any good attachment type for the wood alternatives? Ideally, one would want a strong beam saddle with a bent top that can be "hung" on the support beam, then you would only need to check the shear capacity.

 

[imported_Byggaren]

Why not insert the glulam beam (or preferably an HE-beam for lower construction height) above the bottom chord in the existing truss with support on the gables of the existing building and wedge a shim between the beam and the top chord of the existing trusses? Then you can support the entire truss before demolishing and avoid messing with any connections at all. However, if you still want to do it, noggings between the existing trusses at the eaves are a way to go with BMF construction fittings (Gunnebo Bruk) in the angle between the nogging and the bottom chord side. The new truss will be free-spanning in the other direction and won't be affected by this.

Support for the steel beam can be arranged in the walls down to the foundation with a square steel profile, type: VKR, VVR (cold- or hot-rolled in millimeter dimension) or RHS (inch dimension). This way they are also hidden.
_______________
The Builder

 

[Gugge Grön]

Thank you for your response.
The reason I would like to have the support at the end of existing rafters is that there is a foundation wall below this. You get a very good base for the columns in other words.

I am not quite sure if I followed your reasoning regarding noggins.
Should one install short joists between the rafters with angle brackets, or is BMF-brackets a specific type? (did not find any brackets with that name on Gunnebo's website)
How do you handle the support? Should the noggins be attached to the new rafter/glulam beam?
Grateful for help!

 

[imported_Byggaren]

Nogging between existing truss feet, anchored with BMF construction fittings (type 105 with reinforcement) to them, nailed with anchor nails (or screws) for ½ shear force for existing truss shoe (the other half is taken from the other side). New truss (with reinforced lower frame for current conditions and load from existing truss) nearest existing house (alternatively, a glulam beam instead of a new reinforced truss). To this, the noggings are nailed with a sufficient number of nails (preferably in a nail-glued joint or screw-glued) for current shear forces. (Then you can build a built-up truss on the glulam beam and jack rafters to two planks on existing trusses at the joint p.b.s.)

You can requisition Gunnebo's catalog of fastening elements by phone at 0490-231 00 or telex 3910. The main catalog contains design instructions for the fittings, which you can find in the Craftsman Catalog. Biltema carries a good portion of them. Type 105 is called item number: 19-624 with them. But even better is to hang up the trusses for the new support using a joist hanger, which at Biltema has item number: 19-601. Corresponds to 'normal' or type A/B at Gunnebo with a number depending on dimension.
___________________
Builder

 

[Gugge Grön]

Sounds very good, especially transferring the forces to the glulam beam via a nailed connection with noggings. As I see it, the weak point is still the connection between the old truss and the nogging. The support reaction for the truss is about 14 kN. Is it possible to: 1) Transfer the force via nail to the nogging 2) Can the nogging handle this force when the fitting will be near its end grain? Isn't the risk of splitting high?

 

[imported_Byggaren]

Sounds very good, especially transferring the forces to the glued laminated beam via nail-bonded connection with blocking. As I see it, the weak point is still the connection between the old roof truss and the blocking. The support reaction for the roof truss is about 14 kN. Is it possible to:
1) Transfer the force via nails to the blocking
2) Can the blocking handle this force as the fitting will be close to its end grain? Isn't the risk of splitting great?

Since it will be a single shear joint with 14kN/2 per side, you need to account for 10 nails/screws in each angle against the truss and blocking. Then you end up with a moderate 0.7 kN per nail, which corresponds to a nail no. 43. Not all nails sit at the edges so the risk of splitting is not great. But that was also why I wrote in the second to last sentence: "But even better is to hang up the trusses to the new support using a joist hanger that Biltema has, item no.: 19-601." Then the truss rests in the joist hanger and you only need to anchor it against sliding with a few nails/side.

If you combine both methods, the truss gets both suspenders and a belt in the suspension. If it's an old truss made with fish plates (wood panels) at the joints, it is also better from that perspective to use both since you never really know how the joints are nailed. In the worst case, it's 75x28, fired with a pepper gun, without any thought about where they do the most good. It holds as long as the bottom chord is supported on the plate, but if that supporting base disappears, the nails need to take shear forces they are not calculated for.
_______________
The Builder

 

[zadix2]

Old thread, but I'm curious about how it went?
I'm considering doing a similar extension myself, and have the same options for beam support. I may also be thinking about having a vaulted ceiling in the new part and then also in the existing part... but it might be totally economically unjustifiable...