Built a patio room last year, attached my 4m long rafters to the front beam. Secured them with 160mm 6mm wood screws, a total of three screws per rafter.
Now that the summer heat has hit, a gap of about 2mm has appeared between the beam and the rafters. Is it shrinkage in the glulam, the patio room holds 50°C daily right now, or is the patio room coming apart?
It is probably primarily the glued laminated beam that shrinks in width when it dries in the heat. Skew screwing is not a good method for fastening beams at all. Partly for the reason that you have now discovered, and partly because the fastening in your case needs to handle up to 750 kg per beam. I suggest you get some nice angle brackets with space for lag screws, which you place under each beam.
It's probably primarily the glulam beam that shrinks in width as it dries in the heat. Skew nailing is not a good method for attaching beams in general. Partly for the reason you've now discovered, and partly because in your case, the attachment should be able to handle up to 750 kg per beam. I suggest that you acquire some nice angle brackets with space for lag screws, which you place under each beam.
I really want to avoid brackets; they are usually really ugly. As you can see in the picture, I placed two 45*70 studs underneath for support (to ensure those 750 kg don't tear the structure down). Now that all the timber has shrunk, there's about a 3mm gap between the rafters and the 45*70 stud. It feels like all the wood has shrunk a lot in every direction.
I didn't see those rules. It will probably hold, although you'll get a dust shelf. You would have gotten a more elegant solution if the extra studs covered the entire glulam beam but with cutouts for the rafters. If you're going to use fittings, they should be sturdy and attractive. Common building fittings rarely meet the mark in terms of appearance. I'm attaching a picture that I used in a similar thread the other day. It's a school designed and built by professionals.
Everyone who's seen the build thinks I've overdone it with screws, etc. But I'm cautious when it comes to things and want it to be solid. Most likely, all the wood now has a moisture content close to self-ignition, and the gaps that have appeared have more to do with shrinkage than poor anchoring. But if I find nice angle irons, they'll go in place too.
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