Wavy roundwood rafter & batten roof structure. What are my roofing options?

I had a talk with the guy who was supposed to cover my roof with reeds. He was drunk and without inhibitions let loose his doubts about my way of building my roof and it added uncertainty to my situation going forward.

I would like advice on:
Should I continue trying to build a reed thatched roof or consider an alternative?
  and
If I go another route, what are my roofing options on an uneven roof?

My Roof Situation
My goal is to build a house from sustainable materials as much as possible without nails. Last Fall, was year 3, when I constructed the roundwood rafters and started building the battens from mostly dry wood found in the pine forest until winter came and I left the structure as is until this Spring. I returned to find an abundance of green pine, when they cleared that same forest, which I thought suitable for battens, thus I built the remainder of the front side of the roof using only green wood.

Here are the problems the guy mentioned yesterday:

The battens should be perfectly even from one to the next all the way up the roof. Mine are not aka the roof is wavy

Green wood will warp when it dries

He said: "You should never use dowel joints for a roof construction." Why, I do not know.

Wavy Roof
Having laid down the battens on my first half of the roof, I see why it's helpful to have everything as even as possible and why I've only been able to find information using dimensional rafters, however, I decided to work with what I have and can get access to, plus, building this structure is a learning process for me, full of mistakes and lessons, I couldn't have learned without some kind of experience. He told me last year to try to get it as level as possible and we'd find a way to fix it. Does anyone have advice how to level a wavy roof or how to work with it?

Green Wood, Warpy Roof with Dowel Joints
Here I posted last year how I constructed the roundwood rafters. The battens are pegged with a 5/8" dried oak peg in each rafter. I drilled halfway into the rafters at each joing, at least 4-5cm deep, drilled offsets, which alternate directions left/right going up the roof  and added wedges into both ends of the pegs. I possibly spent the most time on this part of the process.

I would like some additional perspectives. Is there something else I haven't though about that could cause issues,

Hi Maruf,
Your project looks AMAZING! I keep looking at your pictures in astonishment! We had a heavy snow here this past winter and I had a couple of dozen large limbs come down off my juniper trees. So I am letting them dry out and planning to build several shade structures in my gardens that will be similar to what you are building. But they will be tiny compared to your project. And it is not so important that they be structurally sound because they are only for shading my plants.

I can't address most of your questions but I do know a bit about 'green' wood. I have the limbs all leaning against my garage drying out and several of them are twisting and bowing as they dry. That's what wood does.
I have built lots of stuff out of lumber over the years. Back in the day, like 50/75 years ago they used to cut the trees into 2x4s, 2x6s etc. Then they banded them together and kiln dried them for several days. Then they were placed in a building (still banded) where they would continue to dry out and cure for a few months. So the lumber we bought back then was fully cured and most, but not all of it would remain pretty straight.

They stopped doing that decades ago. Over the years they have cut back the curing time even more. Now when I look at lumber at the store I'm pretty convinced it was probably a growing tree a week ago. I pick out the straightest board I can find with the straightest grain to bring home but within days it is starting to warp badly! Now whenever I buy wood for a project I bring it all home and place it on pallets in a really tight pile in the sun, under a tarp. I place a lot of heavy weight on it, cinder blocks and bags of concrete and let it continue to cure for as long as possible before I use it.

That's about all I can tell you. I hope someone comes along soon to give you lots of great advice because I would really like your project to be successful! It's amazing! If our ancestors could find a way to do it so can you! Please keep us posted on your progress.

With the battens where you have them it looks like thatch is your only option aside from metal roofing (with shims for an even surface). At that slope thatch should work great. I have seen photos of reroofing of a medieval cruck-framed house with roundwood rafters (don't recall the shape of the battens/purlins), and it was about as wavy as yours.

You mention that the roofer says you need a flat roof surface for thatch... that may be what he would like but it is certainly not a universal requirement. Thatch is famously adaptable to "interesting" roof shapes.

That looks like a lot fun and a lot of work!  You're living the dream!  I say go for it, the worst that would happen is you live with it for a while, re-roof later on and learn a lesson.  

Could you make wooden shakes work?  Shakes would probably take some shimming and you would have to break your rule for no nails, but it might be worth considering.  Unless... *idea*gasp*... you could hand tie each shake with cordage (haha)!

What about sod?  I know nothing about sod.  Do you need decking under it, or could it just lay out over purlins?

Lots to consider, very interesting.  Keep us all posted!

I think for thatch, the waves nessacary is fine as  you can always add a little extra thatch ti makenit appear even when finished. The pitch looks sufficient for thatch though I have ZERO real world experience with thatch it is my understanding that steep is best

I like your s curve joinery between poles!

Thoughts on the dowel joinery, if that dowel is all that is holding the poles to the roof than my intuition tells me they may be subject to failure from shear force, which is important because even with no snow or rain load you'll have a lot of weight creating shear force on those joints.
With thatch, weight will increase under snow OR Damp as the organic material collects a bit of moisture, especially if you use pine boughs or something of the sort.

Perhaps thicker rafters so you can make a horizontal notch for the purlins?

Maruf Miliunas wrote:Here are the problems the guy mentioned yesterday:

The battens should be perfectly even from one to the next all the way up the roof. Mine are not aka the roof is wavy

Green wood will warp when it dries

He said: "You should never use dowel joints for a roof construction." Why, I do not know.

I see quite a lot of wavy roofs. There are a lot of old buildings here (including my own house) and often the timbers have warped, sagged or were simply not straight to begin with. I have A-frames in my house that were clearly green when they were worked (most are oak, which would have been a nightmare to work dry with hand tools) and they are twisted in every direction.

My feeling is that using thatch as a roofing material will allow you to take out some of the discrepancies. I would imagine that it is possible to use a thicker layer of reed on the areas that are low to give a surface that is better able to shed water. I believe that the fear is either of low spots, which the water may sit in and permeate into the thatch, or simply that it will be more difficult to thatch an uneven surface and that your roofer would rather not have that challenge!

Your roofer is, of course, correct that the wood will warp and move as it dries. If you are concerned about this, particularly at the joins between your battens, you should try and use the driest timber available for that job. Of course, the frame will likely shift over the coming years too. If your roof timbers are large and well joined this should hold the shape of the structure but I would imagine it will shift a bit. If you have the time available, you could leave it exposed for the summer, tarp it up over the winter and work on it next year - the sun and the wind should have taken out a lot of the moisture by then. Personally, especially with the planned thatch, I would press on and try to build some flexibility into anything sat on top of the structure to allow for a little movement - both initially and then seasonally.

As for the comment about not using pegged joints on a roof, could he have meant that, if the roof begins to leak and the timbers expand, the pegs could loosen and jeopeardise the structure?

I've found a few photographs of old roof timbers for you. They aren't likely to be super helpful but you might find them interesting. One shows straight, rectangular batten in the modern style that are sat on hewn square beams. The other shows a more elaborate A-frame with material woven between the many, small rafters to create a ceiling. All of these roofs were covered with tile or slate.

Thank you for all of the replies and support, it really bolstered my confidence going forward with thatched roof.

From my understanding of all the replies is to keep in mind that the weight of a live load on the roof will be a lot, so I will go over and reinforce any joints that give me doubts. The greenwood I would think will tighten around the dry oak dowels, so in theory shouldn't it get stronger as it dries? The roofer had said I can tie with rope, so I have done that in some joints where the rafter dips lower than the adjacent rafters to keep the batten from popping up. All of the battens easily support my weight (roughly 175lb/80kg), is there any reference I could use to know if that's enough? The front side roof slope is around 55º so at the very least, I hope it won't hold too much snow. The back will be less steep and it has fewer rafters so I intend meatier battens.

As for the drying and warping of the wood, the front side uses round wood and I'm unaware of how roundwood warps over time and how that will affect the roof. At this point, and in my current state of naivete I'm thinking to go forward with it, I don't want to cover it with plastic over the winter, some parts of the house like the crucks have already overwintered twice so I'm pretty adamant about getting the roof up this year.

From all the replies I understand that I can add thatch where it's lacking to make up for any unevenness. Would anyone have any resources on how to patch any unevenness with reeds or is it something you intuitively do?

@Gunnar Shakes were my original thought before I learned that thatched roofs don't need a plastic membrane sheet and they are their own insulation, whereas sod definitely needs a waterproofing membrane and a lot of fricken strength to hold the earth.

@Devon What do you have in mind by "horizontal notch" for the purlins?

@Luke The roofer was worried that the pegs weren't tightly pegged, however, I think they are. Furthermore, what is that woven ceiling? It's fascinating and I can't find anything online about it!

The woven ceiling is made from straw. I'm afraid I don't know any more details. It is the Kennixton Farmhouse; originally built in 1610 and later relocated to the St Fagans Museum in Cardiff.

Unfortunately don't have means to draw what I mean so I'll do the best to describe it

It looks to me that the current situation is two pieces of round wood that meet at the outside edge of each circle, connected with a dowel between them. This creates a situation where not only so the purlins want to roll down under their own weight but also as additional we8ght is added gravity wants to pull them down perpendicular to the dowel, whether dry  or green a dowel doesn't have enough shear strength to withstand this imo. It will either shear or pull out.

My proposed solution may require thicker rafters but essentially involves carving notches in the rafters to support the purlins so that they "want to" push into the rafters when weight is applied, I THINK this will effectively transfer the forces into the rafters as intended, rather than concentrating it on the dowels

I think it would look like a MUCH less exaggerated version of what I remember Paul's one log stairs look like

Thanks Luke, and thank you Devon, your explanation makes sense to me. In some places I dug a seat into the rafters so they sit snug but it other places where the battens were thinner, I opted to reduce the waviness by not digging in. Would a tight rope joint suffice, otherwise, I think I could crafter a nook to wedge something in between the two.

I think lashing(guessing that's what you mean by tight rope) can be really sturdy joints, but in my experience with small construction in which I have used lashing, it does tend to loosen over time so you're either creating more maintenance over time to make the task at hand a little easier or you're giving yourself a false sense of security if it's neglected
That's my thoughts anyway, maybe someone else is much better with lashing than I am, and rawhide could be a good option as the shrinkage may prevent loosening

Devon Olsen wrote:in my experience with small construction in which I have used lashing, it does tend to loosen over time ... rawhide could be a good option as the shrinkage may prevent loosening

I've also heard that this can be a problem. I know some who soak rope in water when they want a really strong knot - it dries and shrinks, as you describe with rawhide.

My experience with wetting  (non-synthetic) rope has been that rope swells and becomes tighter in knots and may get shorter and thus tighter in length, then loosens up as it dries.

I think if you were using rope you would want to start with totally dry material so knots can be cinched up tight, and will swell a bit with humid conditions. It is not likely to stay so tight over time, though, unless made from synthetic material.

Of note when considering the weight of thatch on your roundwood rafters, I recall that the photos of the medieval house reroofing (with thatch) showed the rafters as being of roughly similar size to yours, and obviously lasting for hundreds of years. The thing I would be concerned about is the battens and their dowel connections; unless set in some sort of notch in the rafter as you describe, there is a lot riding on tiny pieces of wood that could weaken over time.

Have you seen this Iron Age house build? Here they describe the thatching process.

Thanks for the insights about lashing and for the thatching video Glenn. In that case, I will see what I can do to add horizontal notch support on the existing dubious connections and add them going forward. Because the dowels are set in and removing them may cause more damage, I've been considering cutting out a 5/8" circular notch below the joints to tightly fit in the dowel remainders that are too short to be dowels for support.

Time is crunching and I'm realizing this roof project will likely extend to next year because we have a yurt being made and we need to build a platform so we have somewhere to overwinter and this roof is not something I can or want to rush.

This just landed in my email inbox. Look at how many people are on that roof:



HT to The Last Straw journal, who also put in a link to a great thatching resource that you might already know about:

thatching info - timbers and features

Phenomenal photo Phil, and a phenomenal thatching resource. Thankyou for sharing!

Phil Stevens wrote:This just landed in my email inbox. Look at how many people are on that roof:



HT to The Last Straw journal, who also put in a link to a great thatching resource that you might already know about:

thatching info - timbers and features

That's an amazing photo of community involvement. It takes a village to thatch a roof! Just awesome when people work together like that to help each other. Is this photo in New Zealand?