Budget sloped ceiling insulation

Dear all, hello and thanks in advance for your advice. I am in south west scotland at the moment working on the restoration of a large old stone building which will become someone’s home. The building has 2ft thick stone walls pointed in a sand:cement:lime mix which still enables it to breathe nicely.

I am struggling to find affordable natural insulation options for the internal ceilings which will be covered in old floor boards…i am on a very tight budget. Straw and clay are available pretty much locally.

I have attached a picture of one of the ceilings and would appreciate your thoughts (the sloped ceiling will be exposed— horizontal beams are coming out). I want to use as much natural, recycled, repurposed material as i can and was glad to find you all here! anyone else in scotland?

I have no ideas regarding the insulation.  I would give serious thought before I removed all of the horizontal beams. I suspect they serve a structural purpose.

Welcome to Permies.

John F Dean wrote:I have no ideas regarding the insulation.  I would give serious thought before I removed all of the horizontal beams. I suspect they serve a structural purpose.

Welcome to Permies.

Hi John, thanks for your concern, local licensed structural engineer has been & done calculations, necessary supports being welded from recycled steel and he will check all.

If the ceiling is going to covered with old floor boards why not fill with straw as you add the boards?

Hi Dominique,

Welcome to Permies.

How about wool?

Mike

Anne Miller wrote:If the ceiling is going to covered with old floor boards why not fill with straw as you add the boards?

Hi Anne, thanks for this idea. I was just looking at the R values for various types of insulation (attached), unfortunately the R value for straw by itself seems to be very low which was surprising to me.

There are all kinds of different material that can be used as insulation.

I suggested straw because you mentioned that it was available.

Some sustainable insulation materials can be sawdust, wool, paper or cellulose insulation.

We went with cellulose because we were able to DIY ourselves.  It was basically fine shredded paper.

Something that might work that you might want to look into are panels made from mycelium aka fungi:

https://permies.com/t/mycelium-insulation

If you want natural i guess wool is an obvious one.
Can I ask why the tight budget for insulation?

Hi Dominique,
First... that is a really cool looking building.

Second, how natural and how inexpensive are we talking? Some ideas that come to mind is blown in cellulose. The stuff in the US is often from old newspapers and old bluejeans shredded with some stuff sprayed to reduce bugs and flammability. So recycled... but possible nasty stuff sprayed. Wool insulation has already been mentioned, but again, needs to be treated to reduce bugs and flammability. I personally like the mineral wool insulation... though you could probably argue its not the most sustainable... but way better than most foams and fiberglass. They melt left over slag from the steel making process and spin it into fibers to make bats that look similar to fiberglass, but are naturally bug and rodent resistant and (my opinion, not speaking for the companies) is also fireproof. Lastly (my personal favorite), I know there is a lot of work with hempcrete across the pond. Hempcrete is insulative (though it needs to be a bit deeper than some other options) and is probably available in your area. All of those would allow vapor permeability, but I am unsure about prices. So I'm not sure if they are beyond the budget or not.

I’m also going to go with rockwool for 3 reasons. Weight, flammability and familiarity.

2nd would be straw. However, that is straw that is still bailed. When bailed it keeps its fire resistance as soon as you cut the bails open, you lose that resistance. You could try to keep the bales intact but they will probably be thicker than your joists, making life very complicated. The bailed straw is also very heavy which I doubt your engineer took into account when removing the beams.


If you were putting the ceiling at the beam height, I would go with straw bales. If you go up into the vault, you need the most space and weight efficient insulation to counteract the massively increased surface area (the easiest way to reduce the amount of heat lost through something is to make the surface area smaller).


I also suspect that with a wood, insulation, wood construction that building control won’t look on any natural/flammable options too kindly.

You want that insulation to last at least 50 years and a non-organic option will last longer.

I second the comment about the horizontal beams. My default assumption looking at the photo is those are collar ties and they are absolutely integral to the structure of the roof. Consult an engineer, and be prepared to hear that they are structural.

Also I see lots of little holes on the undersides of many of those pieces...maybe it's just something else misrepresented by the camera but have you verified it isn't carpenter bee damage?

With insulation, consider not just things like R-value, weight, familiarity, resistance to pests, and flammability, but also:

- what happens if it gets wet, and
- what happens over time with respect to gravity--i.e. does it tend to want to settle downward or does it have some kind of internal structure that keeps it rather evenly distributed.

The overall size of the structure and the methods used to heat and cool it may also impact your decision; for example, a small building with a good rocket mass heater can be heated up so well in the winter it might not need very good insulation.

You mentioned 2-foot thick stone walls...How is the building oriented with respect to the equator? How wide are the overhangs from the roof?