This is long, so bear with me !....
So we moved into this 1970’s bungalow in February, a three bed timber frame home with brick cladding, which hasn’t been touched from a decorative perspective I guess since the 1980’s. We have 3 kids, and I work from home, so there are two major changes we need to make:
My original plan was to build something completely from scratch in one corner of the garden, so a blank canvas.
Prior to this work we had a short term need for a shed for all our gardening / bike stuff. The location for this was going to be to take down a “lean-to” type construction which sits on the back of the garage, which I could see had a concrete base, and plonk a pre-bought shed on there (I know, I could build my own, but I have hundreds of jobs to do on the house, so buying one seemed an easy win).
The garage has a sloping metal roof, which condensates horrendously in winter, which continued over the lean too.
First job was to cut the metal roof at the back of the garage, in 30 degrees heat, that was fun.
In taking the roof off I was surprised to find it insulated and boarded inside the lean-to.
Once it was off I then approached the walls, to take them down. As I started to take them apart I found that underneath the tongue and groove cladding was some sort of felt membrane, then solid 4x2, with 30mm of polystyrene insulation in between, a vapour barrier inside, then MDF walls. So what I’d found was far better put together than the outside view / condition had suggested.
The walls also stood on a single brick plinth, with a DPC on it, and under that tied in was a DPM, coming out from under the concrete slab.
Anyway, I decided to continue the deconstruction, to start with a blank piece of paper, and so now all that’s left is part of the plinth, and the slab. Throughout the deconstruction though my mind kept going back to the “build a workshop, Mike’s way” thread, and the similarities of what this construction looked like. This is probably after a >12yr break – amazing what sticks in my mind, planning to copy it – and how useful I thought it was at the time !
Anyway – to the question (taken a long time to get here, apologies!)
From a bit of excavating what I’m left with is what looks like a concrete foundation, with two layers of engineering bricks on top. Within those engineering bricks is a slab, poured to their height.
If I put a timber frame on top of two layers of bricks (I’m going to replace the single layer that’s there now), and insulate the timber wall on top with 100mm PIR. I’m also planning to put 50mm PIR on top of the slab underneath the floor (as I’m not sure if the slab is insulated, and think even if it is it probably needs more). The issue / question I have is, if I go with that approach, then I have a well insulated timber wall, and underneath it I think I’ve got a cold bridge across the brick plinth, at least above the floor PIR, so about a brick and a bit.
I’ve mulled this over a lot, does a small cold bridge matter, do I need to use insulated blocks rather than bricks, do I put PIR on the inside face of the walls, and continue it over the bricks. I’ve done a lot of internet searching to try and find an answer, but everyone seems to be either building cavity walls, or not bothering with the brick plinth at all.
So, has anyone (Mike, and all the other knowledgeable people on here) got some advice on how I can solve this, or even if I need to?
Considerations:
I’m conscious of roof / head-height (it’s within a metre of our boundary)
I am replacing the entire garage roof at the same time, I plan to do it with a flat roof with 100mm PIR across the entire roof, garage and office (I bought a job lot which will do the lot, for a good price)
The garage roof slopes front to back atm, so the office is at the low end (front of the garage is 250cms, back of the garage 216cm, and the garage is 510cm long. So I think I can make the roof shallower and gain some height at the office
I could make the roof slope another way (side to side maybe)
Some pictures / photos:
So we moved into this 1970’s bungalow in February, a three bed timber frame home with brick cladding, which hasn’t been touched from a decorative perspective I guess since the 1980’s. We have 3 kids, and I work from home, so there are two major changes we need to make:
- A fourth bedroom made out of a change of layout (that’s another project)
- An office for me.
My original plan was to build something completely from scratch in one corner of the garden, so a blank canvas.
Prior to this work we had a short term need for a shed for all our gardening / bike stuff. The location for this was going to be to take down a “lean-to” type construction which sits on the back of the garage, which I could see had a concrete base, and plonk a pre-bought shed on there (I know, I could build my own, but I have hundreds of jobs to do on the house, so buying one seemed an easy win).
The garage has a sloping metal roof, which condensates horrendously in winter, which continued over the lean too.
First job was to cut the metal roof at the back of the garage, in 30 degrees heat, that was fun.
In taking the roof off I was surprised to find it insulated and boarded inside the lean-to.
Once it was off I then approached the walls, to take them down. As I started to take them apart I found that underneath the tongue and groove cladding was some sort of felt membrane, then solid 4x2, with 30mm of polystyrene insulation in between, a vapour barrier inside, then MDF walls. So what I’d found was far better put together than the outside view / condition had suggested.
The walls also stood on a single brick plinth, with a DPC on it, and under that tied in was a DPM, coming out from under the concrete slab.
Anyway, I decided to continue the deconstruction, to start with a blank piece of paper, and so now all that’s left is part of the plinth, and the slab. Throughout the deconstruction though my mind kept going back to the “build a workshop, Mike’s way” thread, and the similarities of what this construction looked like. This is probably after a >12yr break – amazing what sticks in my mind, planning to copy it – and how useful I thought it was at the time !
Anyway – to the question (taken a long time to get here, apologies!)
From a bit of excavating what I’m left with is what looks like a concrete foundation, with two layers of engineering bricks on top. Within those engineering bricks is a slab, poured to their height.
If I put a timber frame on top of two layers of bricks (I’m going to replace the single layer that’s there now), and insulate the timber wall on top with 100mm PIR. I’m also planning to put 50mm PIR on top of the slab underneath the floor (as I’m not sure if the slab is insulated, and think even if it is it probably needs more). The issue / question I have is, if I go with that approach, then I have a well insulated timber wall, and underneath it I think I’ve got a cold bridge across the brick plinth, at least above the floor PIR, so about a brick and a bit.
I’ve mulled this over a lot, does a small cold bridge matter, do I need to use insulated blocks rather than bricks, do I put PIR on the inside face of the walls, and continue it over the bricks. I’ve done a lot of internet searching to try and find an answer, but everyone seems to be either building cavity walls, or not bothering with the brick plinth at all.
So, has anyone (Mike, and all the other knowledgeable people on here) got some advice on how I can solve this, or even if I need to?
Considerations:
I’m conscious of roof / head-height (it’s within a metre of our boundary)
I am replacing the entire garage roof at the same time, I plan to do it with a flat roof with 100mm PIR across the entire roof, garage and office (I bought a job lot which will do the lot, for a good price)
The garage roof slopes front to back atm, so the office is at the low end (front of the garage is 250cms, back of the garage 216cm, and the garage is 510cm long. So I think I can make the roof shallower and gain some height at the office
I could make the roof slope another way (side to side maybe)
Some pictures / photos:
