Designing a timber frame building

[Rezi]

All a bit hypothetical at the moment but my next big project could be to build a timber frame building approx 4m x 12m, concrete pad, ground floor use with a loft storage area.
I'm an engineer but I'm not a builder so, I would need to figure out how to spec the correct size material to support the building load. It's not impossible but it would be challenging. Is it feasible to design this myself or should I just employ a professional?

 

[AJB Temple]

That's just a three bay or four bay barn. Not a big deal at all. Fair bit of work to do it traditionally.

 

[Mike G]

Are you talking about a traditional timber framed building, like the old oak frames that were built up to the end of the 17th century? As opposed to a modern "stick built" structure? If the former, then there are very good reasons for the timbers being the size they were, and the joints being designed as they were, and any attempt to alter things could lead to issues . If you aren't 100% confident with this sort of structure, then get someone to design it for you. As Adrian says, though, this is a small span building and so the frame design won't be too tricky. Funnily enough, I've designed one about this size for a self-build client which is on site at the moment.

What is the building to be used for? Designing insulation, external finishes, and openings can be more of an issue than the frame if it is a residential building, and design of the timberwork in those circumstances is mainly about the aesthetics.

 

[Cabinetman]

You don’t say if it’s a workshop, but if it is I would make it – if you can, wider than 12 feet, even if you have to limit the length, in my experience a long thin room and a square room are almost equally limiting. Mine is 5x15 mtrs and I find it a bit long and thin. Ian

 

[Rezi]

To give a bit more info, I'm in the process of buying a property which doesn't have a workshop but does have an open sided 3 bay barn (well done Adrian) which is somewhat ramshackle. I will get the advice of a builder I know but I don't think it's possible to save and convert it. The walls have been spreading under the weight and remedial work has been done to counteract it.

This is the only picture I have.



I would like to replace it retaining the same look and footprint and re-using the roof tiles, if I can. I think I can manage the timber frame design myself but I know next to nothing about keeping the elements out and the heat in other than in Mike's shed thread and I don't know if that's applicable here.

I haven't taken any measurements yet so my size estimate may be out but the shape will be dictated by the existing footprint. My current workshop is about 8m x 4m and the only problem with that is that the door is in the middle of the long wall.

 

[AJB Temple]

The reason why people do traditional timber framing these days is usually for aesthetics: they want to see the frame and joints. Often this involves making a decision whether the visible frame will be on the inside or the outside IF you plan to install habitable levels of insulation.

Most "oak framed" buildings you see thrown up these days are largely fakery, especially the "oak outbuilding / garage" market. Oak frontage, but the entire interior and roof structure in softwood.

I've made several oak framed buildings and I only do them all in oak. That said, I have access to quite a bit of oak. To have an external visible oak frame on the inside and outside (like the one I've just done) creates challenges of weatherproofing, but you wont have that issue. It also uses a lot of wood. To maintain your traditional look all you probably need is some nice oak (or whatever you like such as Douglas fir) timbers where you want the aesthetics, and then a shed load of insulation (even for a workshop) within or cladding the roof structure and walls. Skin often forms part of the structure and Mike will no doubt have lots of examples of such designs. Far quicker, easier and cheaper to make and erect as compared with a traditional frame. I am not an architect or engineer, just a hobbyist, but I have read everything available in English or German on timber framing. I always recommend people visit the Weald and Downland museum too if they are considering making a traditional timber frame. It shows a lot of construction styles.

Hard to tell what your present building is like without seeing the timbers inside. I made a traditional new oak framed building this year, single story but flat roof with a lot of oak joists pegged in, and it took me three months to cut to size, prepare, cut the joints and erect it: just for the frame which is about 7.5m by 4.5m externally. (Was not rushing though and I am a bit slow compared with Mike).

There are timber framing forums, but also a few here who are experienced at this stuff, so I expect we will be able to help. I can point you to credible timber framing books that contain the calculation methods and principles if you like. It's a bit of a black art as you need to make allowances for knots, shakes, cracks, joints (for which there are claculation methods and rules of thumb) as well as all the usual stuff such as s[ans, loadings for weight, wind etc. Most people over spec the structure as the wood can be very variable in terms of what you get in a load, unless you are paying the significant premium for high grade and ready milled timber.

Should be an interesting project if the purchase goes through. Good luck. Adrian

 

[Mike G]

.....I would like to replace it retaining the same look and footprint and re-using the roof tiles, if I can. I think I can manage the timber frame design myself but I know next to nothing about keeping the elements out and the heat in other than in Mike's shed thread and I don't know if that's applicable here.....

Buy in confidence, Steve. We can deal with that stuff here on the forum. Your biggest difficulty with a re-build is what's in the ground. Everything above that is pretty straightforward.

Have a look and see if making it a little wider would be straightforward. An extra 800mm would make quite a difference, and it would still have a small span roof.

 

[Rezi]

The sale will be complete in a couple of weeks or 3 and I'll then be able to get some more pictures of the structure to put on here.
The reasons for preferring this type of construction are not aesthetic as only visitors will see it but I want it to retain the 'barn' look as it will fit in with it's neighbours and also, it will give me a chance to have a go at something new and challenging.
I won't be doing this in Oak as I can't see any justification for the expense. I'm not pressed for time other than getting my workshop set up so it'll take how long it takes although I wish I had a chain morticer to speed things along.
I know a Welsh guy who lives an hour away from me who has just built a brick 3 bay barn with a timber roof and he mills his own wood from his own woodland so I'll be asking him for advice too.

 

[Rezi]

OK, I picked up the keys a couple of days ago and managed to get a few pictures of the barn structure. I had a better look at it and I spotted that one of the posts in the corner was completely missing the lower 150mm which had rotted away (no pic). I believe that has caused the adjacent back wall to push out and is why the roof apex has sunk at that end. Apart from that, the other posts are also in direct contact with the ground and are in 'OK' condition despite this, the roof structure looks like it is held together with the spider webs and the entire brick gable end wall is straight but is out of square by about 300mm over 5m and looks like it was built that way. I'm no expert but that all seems a bit terminal.

 

[AJB Temple]

Well, congrats on buying the house.

That building looks pole barn rustic. Minimal structure, general absence of joinery in favour of nails in places, and all in all a structure of pole barn simplicity erected at minimal cost.

I have no idea what the planning considerations are in your country, but subject to planning rules my instinct would be to take that building down, saving as many materials as possible for re-use, and build it again properly with proper foundations, walls and insulation. Cheaper and quicker and better to do that rather than fix a myriad of problems.