7. Wall framing
Since making this video I’ve got a whole lot better at creating slides and images so we’ll put some meat on the bones below the video.
Hopefully this is a lot clearer. A couple of differences from the video:
Noggins
You could argue that these aren’t necessary for a single story height. It’s up to you if you add them in like I did. Some people forgo this step and others add two or three between studs. You can offset them like I did which makes them easier to attach or have them in straight line by nailing/screwing at an angle. If you are going for wool insulation in your walls, it might be worth keeping the voids consistent in size to prevent waste.
Window trimmer studs
You can save some timber and potentially use up any off-cuts by splitting the trimmer above and below the sill plate of the window. It will be just as strong.
Headers/Lintels
To ensure we have our bases covered, this is an alternative way of creating the header. The header is still doing its job of transferring the weight of the roof down the trimmer studs.
The benefit of this method is that you can wait until you have the doors before putting in the top sill if you’re not sure of the height. The top sill can just be toenailed into the trimmer studs as it’s not load bearing.
The bigger issue is that, unlike mine, most garden rooms are built under the 2.5m permitted development rule.
If this is the case, your walls will be shorter and there might not be space for cripples at all so you’ll likely have the header butted up against the top plate and the top of the door will reach the underside of the header.
Sometimes even doing the above doesn’t provide enough height for a 2.1m door so you may have to resort to replacing the top plate with the header itself.
The problem is that as the top plate contributes to the depth of the header, we’ve effectively reduced the header’s strength which leads us to the next section.
Note: For longer headers you’ll want wider support on either side so instead of one trimmer stud per side, you may want to double up. For seriously wide openings you may want to opt for three.
How thick does my header need to be?
In the video I gave a rule of thumb:
- <1.8m wide opening: 2×6″ header (x2)
- >1.8m wide opening: 2×8″ header (x2)
But what do you do if you want really wide bi-fold doors, 3, 4 or 5 metres across? I’d love to be able to offer a clear and simple calculation but I’m yet to find one. I do know that it’s not as simple as the width of the opening though and instead factors include the dead load (weight) of the roof and the length of the roof joists as these contribute to the weight the header needs to bear.
Steel headers
It would stand to reason that the width of the header needs to keep increasing the wider your doors are but as we’ve seen in the section above, this eats into your door height so instead we need to introduce some steel!
RSJs
You could go all out and put in an RSJ. These steel beams hold up whole houses so are certainly up to the task. The bonus here is that for a lot less depth you can span a lot more opening! You’ll need friends to lift it though!
Flitch plates
These are thin lengths of steel that sandwich in between the two header timbers and make an altogether stronger combination. This place sells them.
Concrete lintels
These come in many different forms and could be a good choice for shorter openings.
Hang your joists
Rather than having your joists sit on top of your walls you can instead hang them to the inside of the walls using joists hangers. The benefit of this is it allows you to extend the height of the walls without increasing the overall height of the building. This means that you can install a good size header and hang the joists of that instead. The disadvantage is there’ll be no joist overhangs, at least above the doorway.
If I ever find the thresholds for these I’ll come back and update this section but generally speaking if it feels strong and there’s no sagging, it’s probably good enough!
Is OSB sheathing a requirement/can it be added later?
You can save yourself some time and money by leaving the studs bare. The OSB does create a more rigid structure preventing movement and racking, but it’s not a must-have. The plasterboard and battens/cladding will help strengthen the structure as will adding in more noggins so the choice is yours on this one!
You can wait until a later point before deciding by attaching the OSB once the walls are standing. This will also help lighten the walls if you don’t have a bunch of young lads to help! The other advantage to adding the OSB later is you can fix braces from the outside instead of/as well as inside to keep the wall standing while you complete the rest.
How to attach timber walls to a concrete base?
1. A concrete nail gun – no pilot hole needed. With these they will punch a hole through your wall’s bottom plate and into the concrete. I’d say this is best suited for partition walls that hold no weight than your outer structural walls.
2. Drill holes into your concrete and fix masonry bolts or screws through your bottom plates into the concrete. Not a bad but the masonry bolts may crack the edge of your concrete. You’ll also probably want an SDS drill for this work, a combi drill even with hammer action will take a long time.
3. When pouring your concrete base you can insert threaded rods into the concrete along the edges. This requires you to have worked out where the gaps are between studs for all your walls beforehand and you have to do it at the optimum time. If the concrete is too wet, they’ll flop over. Too hard and you won’t get them in. If you manage it successfully you can then drill holes in the bottom plates at the correct intervals and lift the wall on to the threaded rods (heavier work than just erecting a wall). Then you can add a big washer on top of the threaded rod and a heavy duty nut. The walls won’t be going anywhere.
4. This is my preferred option and it mixes methods 2. and 3. together. Once your concrete has cured drill holes wider than your threaded rods. Insert the threaded rods and use resin in the rest of the hole to hold it the rod in place. This is strong stuff and cures quickly so make sure the rod is vertical. Then finish off as in option 3.
Yep, a timber floor is easier!
Now you understand wall framing: how things fit and attach together. You’ll need to watch the rest of the series before starting the walls to understand the choice of sloped joists vs furring strips and warm roof vs cold roof. If you have done here’s your task:
Task: Calculate the timber and header quantities and place an order for delivery. Begin by marking out the top and bottom plates and start filling in the gaps with studwork, ensuring you have your spacing correct for sheet material. Bust out the pizza and beers to get help from your friends to lift the walls into place and make sure you have your braces near to hand to keep them vertical while you assemble the rest of the walls.