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This house has a roof with reinforced concrete beams and ceramic tiles. It's located in Castelo Branco, central interior Portugal, which can get very cold in the winter nights and very hot in the summer days.

The roof currently looks like:

Attic

It only looks bare in the attic, is a small portion of the roof, currently the rest is covered with wood planks that will be removed when the project starts

Attic video with better lighting:

Attic GIF

Ideally the attic will be open as shown on the model below, the attic being the brown platform.

House model

And if it matters here is the roof shape

Roof


I have been reading about how to isolate the roof and concluded that I should have at least 3 layers:

  • Impermeable canvas,

keep any water leak on the outside and prevent airflow

Current choice: Polyethylene geotextile fabric.

  • Isolating material,

Provides the thermal buffer

Current choice: XPS boards 50mm thick (extruded polystyrene)

  • Cover

Protect the isolating material from the inside

Current choice: Simple plaster boards (13mm).


While reading I saw many people focusing on R-Values, here I don't have to comply with any legislation so I am just looking to get the best isolation for the least money.

Due to comments I used this calculator and got a R-value of 10 for the insulation layers mentioned above.


Currently I am not entirely sure how I would attach any of this to the roof.

I read that I could carefully drill the concrete beams, that would not impact its strength if it doesn't drill into structural iron rods on the inside, but I wanna avoid that at all cost.

The main idea is to hook into the concrete beams and then attach the materials to the hooks.

As shown on the following picture although inverted

Example

But there are wood boards on the roof outside the attic that are used to attach the wood planks (with nails) that make cover for the roof on the living area, this could be used to attach the insulation.


Are there obvious flaws on the choices made?

I'm looking for guidance on a general level, could be just material choice, layer design, material attachment or all the above, depending on your expertise.

Note: Keep in mind that any insulation is better than none, currently air is free to move, even in the covered part of the roof, with the wood planks, there are some cracks and a large hole, and the attic is only separated from the living area by a slim plywood and a hole as a door. So if you have different suggestion altogether let me know!

It's also noted the fact that the roof might not take the extra weight, is definitely something to consider since roof is better than no roof and I will have people looking into it before I do any work.

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    where in the world are you? Are you sure the beams are concrete? Concrete is a lousy choice for roof beams. Also you pic is very dark and shows very little detail. Please provide a better pic.
    – RMDman
    Mar 19, 2023 at 13:19
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    Are you going to use the attic as a living space? If not then you just need to insulate the floor/ceiling of the living space below. R-values relate to heat lost/heat gain in a space, most non living use attics just need ventilation
    – crip659
    Mar 19, 2023 at 13:19
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    What is your climate? Regardless of lack of legislation, R-values can make a large difference to your building comfort and operating expense if you either heat or cool (or both) the building.
    – Ecnerwal
    Mar 19, 2023 at 13:19
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    @Ecnerwal I could try to calculate the R-Value, but what I meant is that I want to isolate the roof as well as I can within the budget, the roof is the only concern since the walls are 70cm thick schist stone and concrete. windows will be changed in the future.
    – Barreto
    Mar 19, 2023 at 13:42
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    Best choice of material depends on availability that varies from country to country (what is made or imported and how it is marketed and sold) and on the common practice and skills of local workers. Regulation is often a good guide to best practice. Don't be too contemptuous of regulations. You don't need to follow them blindly, especially if they are not in force where you are. But you can imagine that some of the regulations in places near you are based on best practices, or what SHOULD be best practices, and if you have no other guide, it's a good starting point.
    – jay613
    Mar 20, 2023 at 14:45

1 Answer 1

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+25

I interpret your question the way that you aren't sure on how to improve your roof, and now you look for ideas and confirmation of your current plan.

As much as you'd want to avoid it, for structural work I'd get help from an expert in this matter. Reusing the current load-bearing structure (pre-stressed concrete bars in horizontal layment for the roofing is something new for me) with an new, possible heavier roof sounds too risky for my liking.

Many jurisdictions have also some incentives (tax deductions, state contributions, cubature bonus etc.) to motivate people to renovate by the book. I can imagine that this also could be an possibility for you.

Speaking from personal experience: Relatively to the current building costs, it was very cheap to hire an licensed technician. He inspected my house, made suggestions on how to improve it, helped me navigate the red tape and made all the paperwork for compliance plus contributions.

A good advice I got at the beginning of my building project

"Don't do it piecemeal, either do it completely or don't do it now"

Update

I'll make a couple of points, but I doubt I'll be able to organize this coherently

Drilling the concrete "beams" is an no-go. It isn't only the steel in the "beams" that provide strength, but also the concrete. Better clamp them, or use wire.

The "bad insulation is better then no insulation" is a fallacy. Bad insulation can lead to moisture and mold problems.

Perhaps, just as an brainstorm idea, see this as an repair: Replace the tiles, plug all the holes and do the great overhaul later. You can reuse the tiles when you do it thorough.

Also the "wind load is of no concern" is a fallacy: Once you touch it, you are responsible for everything that happens. Therefor get someone in authority to check it.

I have no insight in your local code and regulation, but at my place an invoice for "maintenance of the load bearing roof structure" from an licensed timber framer is good ammunition for an eventual legal battle, as he is now the responsible one. Try to leave a paper trail for the things that are in your favor.

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  • Its not out of question, thanks for the recommendations, I have looked into a environmental fund that helps with costs into renovating insulation in a house, not sure i will get that since it ends up at the 30th this month. By roof you mean just the insolation layers mentioned right? you think it could be too heavy? that's something to consider, although the roof is about 15/20 years old, didn't think the light weight insulation could cause considerable stress on the structure. vote up either way thanks for the advice
    – Barreto
    Mar 22, 2023 at 13:05
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    With roof I intended all the layers. I can't speculate if your future roof would be too heavy. I just wanted to say that if you are changing it, have someone in authority look over it.
    – Martin
    Mar 22, 2023 at 13:21
  • I understand. thanks
    – Barreto
    Mar 22, 2023 at 13:22
  • @Barreto I know that Portugal is mostly coastal so you probably don't get a lot of snow load, but wind load is definitely something to consider. Any addition to the weight on the roof needs to be carefully considered to avoid the roof becoming the floor. :(
    – FreeMan
    Mar 22, 2023 at 15:26
  • No, snow load is basically 0, there is snow from time to time but not in great quantities as far as I am aware. wind could be very strong in the area but this is in the middle of a village and the house is lower than all others around so I guess its not so bad.
    – Barreto
    Mar 22, 2023 at 22:26

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