Insulating our home in northern Portugal
Strategy, materials and our DIY approach
One of the next things we need to think about is keeping our house warm in the winter. The plan is to insulate the walls and the attic and get some kind of heating system, either a log burner, electric heaters or both.
Portugal is known for it’s great weather, the Algarve region in the south enjoys an average of 300 days of sunshine each year! This is obviously not true of the entire country and winters here in some places can be cold and wet. In the north of Portugal, where we are, temperatures in the winter months average 7-8 degrees Celsius. Porto which is an hour away is the wettest major city in Europe with a Mediterranean climate.
Despite these cold temperatures Portuguese houses often have little to no insulation and outdated or inadequate heating systems. Not all houses are like this, but this was true of the ‘fixer-upper’ type houses we were looking at. We knew this before looking at properties and factored it into our rough budget for house upgrades.
A typical older house in rural Portugal will have a mixture of stone and hollow clay brick walls. These are referred to as solid walls, they have no cavity. The stone walls are left exposed and the brick walls are rendered on both sides.
Why insulate our house?
Our house has no insulation on any building element. Heat is lost through the walls, floor, roof, windows etc. By installing insulation it will be easier to maintain a steady temperature within the house and spend less on bills to heat it.
Internal vs External Wall Insulation
For solid walls there are two ways to insulate, internal and external insulation. There are various guides online discussing both options. I’m going to focus on our strategy and our thinking behind it. For our house we are going with both external and internal insulation.
Let me explain. Overall, insulating externally is a more efficient way of insulating. You are effectively wrapping the entire house in a continuous blanket and creating openings for doors and windows within it. Internal insulation is interrupted by intermediate floors and internal walls so it is not continuous causing thermal bridging in these areas.
Another benefit of external wall insulation is that it doesn’t use up any internal space, but being external means that any original features will be covered up. For older properties this might be more of an issue, our house has few features that would be missed if covered up!
Our external brick walls are covered in a sand and cement render (as far as I can tell), this render gets wet, then dries out in the sun. Here we are planning to externally insulate using a system referred to as ‘capoto’ (also seen with a variety of spellings), perhaps more commonly known as ETICS, EWI or just simply external wall insulation. We will clean the existing walls with an algicide to remove any existing mould and mildew, then attach a base rail to support insulation boards that are then mechanically fixed to the wall with plastic plugs and nails within wall plugs. These boards are then rendered with various layers and mesh is placed between these layers for strength.
Externally we are not insulating our granite walls, but leaving them exposed. Internally we are planning on using some kind of lime based hemp insulation plaster TBC. Covering up the granite seems like sacrilege, it’s not looking it’s best right now, but with a good clean and some lime mortar pointing we’re hoping it will look good. Detailing around the junctions between the external insulation and the stone will be tricky. The walls will be in different planes, and as the extension will eventually be insulated externally, it’s not just on the horizontal plane, but vertically too.
What materials are we using to insulate our house?
There are several options to choose from when it comes to the insulation type. The most common in Portugal are EPS (expanded polystyrene), XPS (extruded polystyrene), mineral wool and cork. There are others like wood fibre, hemp etc but they are not as commonly used or easy to find.
The most eco-friendly approach would be to use cork, which is found here in Portugal. Less miles to travel, more sustainable, but more expensive and sadly not as good as the oil based products. Based on the prices from the supplier I am planning on going with, cork boards at 100mm thick would cost €48 per square metre, this compared to 100mm thick EPS boards is €8 per square metre. From this supplier cork is 6 times more expensive! (There are cheaper places, but the price difference is still significant) To add further cause to going with EPS over cork is that EPS is more thermally efficient. The EPS I am looking at has a u value of 0.031 W/(m².K) whereas cork has a u value of 0.036 to 0.040 W/(m².K) (the lower the better).
Ideally, I would use cork or wood fibre, but the cost is too high for my budget. So, EPS is what I am going with for the walls.
In the attic space I am going to use mineral wool, typical loft insulation that can be rolled out easily over the space. Having been up there recently, it needs a good clear out and clean beforehand. I’m not looking forward to it!
Do the walls need to be ‘breathable’ or vapour permeable?
The one topic that seems to dominate Facebook DIY groups in Portugal is breathable building materials and where to use them. I understand that when materials contain moisture, this moisture needs to escape. If it doesn’t then damage can occur to the building fabric, cause mould and as some people will tell you . In our case yes and no. We have two types of wall construction, solid granite walls and solid brick walls with sand and cement render. The granite walls in our property will not be insulated externally, but will be internally. These granite walls have no DPC so they will inevitably hold moisture, this moisture needs to escape. By leaving the external face exposed, repointing it with a lime mortar and having a lime based finish internally we hope that we can maintain vapour permeability and prevent structural damage and mould etc…
Doing the work ourselves
If I haven’t mentioned it before, we are planning on doing all of the work ourselves. It will be our first time doing it, so YouTube video tutorials will definitely be needed. We have bought some scaffolding, ladders, the correct tools, sponge floats, trowels etc. I think we can do a good job.
It’s likely that I have got some of this wrong! If I have please let me know in the comments, it could help me from making a mistake!
Thanks for reading,
Michael