Friday, 8 September 2017

Building a pole barn

When we moved here there was very little by way of outbuildings. The need for adequate under cover space on a smallholding is very important whether that is for storage, workshop activities or animal housing. Since we have been living on our holding I seem to have been constantly building things. One big (for me) project was building a timber pole barn to replace a dilapidated corrugated steel structure which had collapsed in on itself. 

Here's how I went about constructing a 9.4mx3.6m (about 31'x12')  pole barn from scratch without any previous building experience.

A pole barn, as its name suggests, uses vertical posts as the main supporting structure around which a framework is built. This one is fairly small as far as pole barns go but big enough for my purposes. One advantage is that the construction principles are relatively simple and it is possible with a bit of ingenuity to build it single-handed. If you have friends, all the better.

From this:-                                          To this:-

The first step was to clear the area and mark out the outline of the barn. This is best done using traditional batter boards to square the outline. These allow the guide strings to be adjusted along the horizontal strut. To ensure the outline is square make sure that the two diagonal lengths measured corner to corner are exactly the same.

I used 10 3.5m posts that were 7" x 5" in girth (excuse the mix of metric and imperial).  Six inch square would be more orthodox but these happen to be available at a good price at the timber yard I use. Each post was buried 3 feet deep. An alternative approach would be to build cement foundation piers and bolt the posts on to them. This has the advantage of minimising the risk of posts eventually rotting by keeping them out of contact with the ground. However, this would reduce lateral stability. The decision to bury the posts in this case was because of the sandy, free-draining soil I have making rotting less likely. I also noticed that the surviving posts from the old structure I dismantled had not rotted and these had been in place 40 or 50 years. As a precaution the section of the pressure treated posts in the ground was painted with tar. They were also placed on top of a bed of gravel and more was used to top up the post hole where the post entered the ground.

Horizontal 6" x 2" bracing timbers (called girts) were fixed around the outside of the posts. These provide lateral stability as well as supporting the outer cladding. The girts acting as the top rail at the front and the rear which support the rafters were fixed in place with 10" bolts. The top rails also provided the final height of the barn front and back. At this point I used a chain saw to take off the surplus lengths of the vertical posts. 

Further framing and the rafters were then added. The height of the barn is 2.4m sloping back to 2m.

Heavy duty feather edge cladding was used for the sides.

Purlins were fixed at 60cm intervals to the rafters. Corrugated steel sheets were used for the roof. They were fixed using 60mm Tek Screws for which you can get a screw bit for your electric drill. They go in easier if make a pilot hole with a nail and a hammer. Remember to screw them into the ridge of the corrugation, not the valley, so as to avoid leaks.

For the floor, as a cheaper alternative to cement, I used lump chalk compressed down with a whacker plate. I gather stables quite often use chalk floors as it is softer for horses' legs. I needed 7.4 tonnes of chalk creating an 8" layer which was compressed down to 6". (If you are interested, to get 7.4 tonnes of lump chalk from where it was dumped 100 yards to the barn took 45 barrow loads, 20 shovelfuls per barrow).

One end of the barn was sectioned off and doors added for storage space. The rest of the barn was kept open plan to maximise flexibility of use. I mainly use it for lambing and for storing hay.

Disclaimer - I have no building experience nor been trained in structural engineering. The above is a description of what I did and not necessarily recommendations.

1 comment:

  1. Great barn, I'd love something like that here. I'd love some open stable type areas and maybe a closed off space to keep all the equipment that comes with keeping animals.