This is a thorough step-by-step guide on how to build an A-frame cabin. Well, almost an A-frame cabin as there are short vertical walls on both sides. Here’s a teaser of the finished cabin before diving into the long and arduous journey of the build itself:
Let’s rewind a bit. The building of the cabin started in August 2018. We had some misfortune with our real house and decided we want to have a space to stay in with minimal hassle with bureaucracy. The solution was to build a 3 * 4 meter “half-warm” cabin, which doesn’t require a building permit in our city, Kirkkonummi.
As with every good story, this story starts with a saw. We had already checked that the place that we chose didn’t have any larger trees, but there were a lot of bushes that needed to be get rid of. Once the site was cleared, we built a wooden frame of 3*4 meters (or size of the cabin) in order to find the exact digging spots. Obviously the points were measured (and cross-measured!) as well, but the frame helped to outline the shape and desired orientation of the cabin. Well worth the 15 minutes it took to make.
The started the digging. The ground freezes during winter so we had to get deeper than the frost and into the sand. We dug 9 holes approximately 60 cm deep (the ground is quite sandy so should be enough) and filled them each with 25 kgs of concrete. Inside the concrete we placed bent 8 mm brush steel rods with the ends sticking out from the top. While the concrete was still wet, we placed the first LECA block into the concrete and with a spirit level double checked that it was level. Rinse and repeat 9 times. The clearing, digging and casting of the concrete was surprisingly slow, I believe it took around 2 weekends from 2 people.
Once the foundation was done and concrete dry, the next step was easy; piling the blocks on top of the first block.
Once all of the foundations for the pillars were ready, it was time to cut them to measure. We used a laser level as it was already dark enough outside. We used a combination of angle grinder, a regular saw and axe to cut the final blocks to measure. (230mm angle grinder would have done the job! 115mm didn’t reach far enough, so we had to improvise.) After the pillars were at the same level, we filled the hole with mortar with brush steel rods inside. Finally we measured correct places for steel post shoes that were cast inside the mortar.
On top of the pillars we put pieces of bitumen sheet to avoid moisture of creeping capillary from the pillars into the structural timber. The first planks were 48 * 98mm set flat and the frame itself was made from 123 x 48 mm timber.
After the base frame it was time to cut and attach the structural timber for the floor (123*48 mm). The width of the structure is 3,1 meters and the planks are exactly 3 m long. The gap between the pieces of timber is standard 60 cm. All the joints are made with a combination of nails and torx-screws. The screws are faster and easier to attach, but nails have a much higher resistance to natural movement of the timber and the strain it causes.
The walls were 125cm high, the original idea was to fit the exact height to width of standard plywood + railing + floor board. However, later it turned out that spruce plywood, which is mainly used in hidden structures, is 120 cm wide whereas birch plywood, which is more polished, is 122 cm wide. In the end we had to saw a couple of cms out of each plywood, but otherwise we’ve been really happy with the height of the walls.
The angle of the roof is 66 degrees, which was a pain to saw with a circular saw as the angle in the machine doesn’t go that far.
At this point the winter arrived so after fitting the roof triangle we took it down and laid tarpaulin on top of the structure for winter. Time to hibernate.
2019 came and as soon as the weather allowed, we continued the build with new energy.
The roof triangle were built on the ground and then lifted to place. In theory it’s possible for one (wo)man to do it, but it’s somewhat tricky so it’s a lot easier with 2 people. The triangles were attached to the walls with angle irons. The location for each triangle was the same as with walls and floor timber. So basically each combo formed an individual “frame”. The inside skeleton consist of 8 of these frames (The places measured in cm: 0, 10, 70, 130, 190, 250, 310, 370, 430, 440). Notice the double structure on both ends. The seemingly random horizontal boards seen in the picture helped to measure the right width between each of the roof triangles. It is crucial that the same gap width continues all the way to top, otherwise fitting the inside plywood is going to be impossible.
The structural timber should be double (48mm timber, ~48mm insulation, 48mm timber) on both ends or otherwise the inner panels don’t have a surface to be attached to. The front facing wall is 123mm thick, so there’s ~2cm surface left for the final plywood inside. The front facing timber seen above are cut narrower from the end and go through the double layer described above. This gives the frame extra structural integrity.
Our cabin is going to have a small (1.2m) porch, so the structure continues past the door and front wall.
After framing it was time to weatherproof the whole structure. We used breathable Tyvek fabric, which was really fast to apply. We attached the fabric from outside with rivets..
… and then secured it with 48*48mm laths. The gap created by these will work as a ventilation airway as well. The warm air that rises up should escape from both ends of the triangles just beneath the roof cover.
The roof is very steep and from the highest point the dip to the ground is > 5 meters. My solution was to loop a rope over a sturdy enough branch and use my climbing harness while working. This was (not surprisingly) a bit of a hassle but an absolute necessity. Oooh the lucky people with scaffoldings.
Once the cabin was weatherproof, the hurry subsided. This felt like a proper milestone and the skeleton started to resemble a building. Once the cabin was sealed with fabric, up went the plywoods. I realize now that working on the roof got progressively harder as I leveled up:
- Level 1 = fabric (easy).
- Level 2 = plywood (intermediate).
- Level 3 = bitumen membrane (expert).
Before setting up the plywoods, we added one more supporting rail. The plywood was only 6 mm thick, so it was quite easy to handle but not as sturdy or durable. As the supporting rails were ~ 40 cm apart it worked fine for this purpose.
The first thing we did before starting was to attach a supporting rod on the lower edge of the roof. It was easy to lift the plywoods on top of it before fastening them with screws.
Otherwise it was quite easy. The final narrow pieces on top were a bit tricky. I was hanging from the rope with my climbing harness and crawling on top of the finished plywood area (which, surprise surprise, doesn’t have anything to hold onto with your feet).
At the same time with plywood installation, we nailed Hunton windproof boards to the bottom of the cabin. These were fortified with 48*23mm pieces of wood.
Then started the arguably most gruesome part of the build. The heavy bitumen membrane rolls combined with steep roof and no scaffolding caused a bit of a headache.
We started the process by attaching 48*48 timber into the plywood to function as steps. Then we lifted the roll on the first step, after which I climbed to the same level and wrestled it up to next step and further into the ridge. Once the roll was on top of the ridge, I carefully opened it and let it slide on the other side until it reached the lower edge. Once it was straigthened I let it roll down on my own side (not so carefully).
These tarmac membranes get wrinkled very easily during the installation process so double check that they’re straight. Especially with steep roofs where the roof itself is “the thing” it looks ugly is it’s all wrinkled up. Then it was time tp just nail them from the glue surface before attaching the next piece on top of the glue part (this is a horrible explanation. I’m sorry. You should probably check the installation guide that is attached to every roll..)
After the roof was finished there was a longer pause on the construction and I had a moment of distraction. I was walking inside while minding my own business and stepped on top of the wind shield (thinking it was regular floor…). Even though I fell only only ~1 meter, I fell straight on top of the floor plank with full force. The short fight of My chest vs. Timber plank ended 0-1. After the impact I had a bit of trouble breathing so Heidi called the ambulance and I was rushed to the hospital were they diagnosed a punctured lung. Later I learned that I was actually lucky as the puncture wound wasn’t too far from my heart.
Lesson: Floor is floor. Windshield is not floor.
After the fall I had to lay low (literally) for a while. After I had healed, we continued the work.
Next up: insulation of the floor. As we wanted breathable materials, we used cellulose insulation. This insulation was meant to be blown with a special blower machine, but we mixed it up with a power drill and a whisk-thingy. It worked ok, but if I had to redo this, I would’ve done the floor with insulation “mats” (like we did the walls). Even though they’re a bit more expensive, they don’t whirl that much and they’re faster to apply. This type of insulation makes sense if the area to be filled is over 40 cm thick.
After the whole floor was insulated, we covered it with breathable Ekovilla airtight paper. The seams were taped and the edges of the paper were lifted a little bit on the walls to overlap with the airtight paper in the walls. The supporting rails for the floor boards were screwed on top of the paper.
Each board was first put to their place roughly by hand and then hammered tightly to its place with a short piece of floor board. The screws were hidden on the tongue side of the tongue and groove floor boards (= ponttilauta. Just guess how long I had to google to find the term in english. What the hell!?).
As the wood expands, it’s important to leave a ~ 1cm gap on both ends of the boards. If the initial wall measurements would have been exact (1220mm plywood + 28mm board + 22mm board), this structure could have easily been done without molding. Next time. After everything else inside was finished, we treated the floors two times with osmocolor oil wax.
Once the flooring was done, we moved to insulating of the walls. Insulation was straight-forward as the blocks stayed nicely in place while we stapled the paper cover on. We had help during these days (shoutout to Sofia & Greg!) and it took less than a day to put it all together.
Once the airtight paper was on place, it was time to install the windows. As the cabin is quite far from the road, I had dreaded the operation. Luckily I managed to gather a collection of virile men (Cheers to Lauri, Roope, Eeki and once again Greg!) who carried and helped to install the windows. I’m guessing the bigger one (180cm x 160 cm) weighed around 100 kgs as it’s double-glazed with thicker safety glass inside. The installation itself was easier than I had thought. You should level 3 screws underneath and basically just put the window on top of them. Of course it’s always nice if you have time check that the window is straight. The internet is full of installation guides, so I’m not going into more detail here.
After the windows it was time to the install the door.
Once all of the holes were sealed, we started the final phase: installation of the 9mm birch plywood. We set up a temporary working station inside, where we cut all the plywood into measure. We used a circular saw and a “guide board” with wood clamps to cut the plywood into correct shape and size.
The plywood is heavy and as it is a very confined space with ladders and different kinds of stands everywhere, moving a sheet of 120x270cm plywood isn’t easy. Luckily we had help (Lauri and Ia one day, Sofia and Greg the other). It’s possible to lift them into place with just 2 people but it’s a real pain in the ass and takes time. 1/5 stars, not recommended. So better try with a little help from your friends. It’s easier to lift them high with a little help from your friends.
We “moved in” (well not really, it’s our weekend cabin) in October 2019. The cladding wasn’t finished yet, but inside was done and the cabin was already insulated and weatherproogf.
We had left the front cladding last. It was the trickiest part and working there meant trusting my life to an old rope and not-so-steady ladders. You would think one would learn from a punctured lung. Well, think again.
So that’s about it. There always some work left to do, but the cabin is now habitable and it performed the first winter well. We have a radiator inside to heat up the cabin and if it gets really cold (-10 to – 20 Celsius) we light up our small ethanol stove.
Thanks for reading, hopefully you’ll stay around to follow our adventure of building the “larger cabin” aka our proper house.