I’m building steps from my house to the garden, where previously there was decking. I’ve already poured concrete for the steps base, leaving underneath a layer of MOT sub base which I compacted. Plan was to use Class B Red engineering brick 2 layers per step and put a concrete paving slab on top, 2 steps total. For filling up the the hollow area I bought Aerated blocks and was going to fill the gaps with more hardcore and concrete - I do not have a concrete mixer, only a drill with an attachment so this made sense and would save me a ton of work.

A friend of mine was visiting and saw this and pointed errors to what I was doing:

  1. He told me I should use some insulation between house and the steps so that moisture doesn’t raise through them inside
  2. He told me that the aerated blocks I wanted to use as a filler are like sponges and will hold water and make the problem with damp even worse, he suggested I use salvaged bricks instead

Removing the concrete base is not an option now, so I want to ask if what he's saying has any merit - should I put some insulation between my construction and the house wall? Or should I insulate the bricks from the concrete base? And what about the Aerated blocks, should I replace them for something else?

Including rough top-view and front-view sketch of what I'm doing, which was used to help me estimate how many bricks I'd use

top and front view sketch picture of the base foundation for steps

  • 1
    I am getting confused about what materials you are using and the layering of each. Can you provide a sketch to clarify?
    – r13
    Commented May 15, 2021 at 13:05
  • Insulation and moisture barriers are very different things. I suspect we're discussing the latter. Does your climate freeze?
    – isherwood
    Commented May 15, 2021 at 13:15
  • @isherwood , According to the links he provided, he is in the UK, very wet as you may know...
    – Jack
    Commented May 15, 2021 at 16:14
  • @r13 I've included a very rough sketch, it is wrong though because it didn't include the slabs which would rest on each level of bricks - I don't want to cut slabs so the top step would be elevated by the slab's height. I've also used it to estimate how many aerated blocks to use for the inside construction - it was supposed to fill it with no gaps using blocks and concrete
    – kacpr
    Commented May 16, 2021 at 16:01

2 Answers 2


If the base for your stairs are not at the same level in ground as your foundation for your house, your stairs could or will be subject to frost heave. For that reason a thin layer (1/2") of insulation between the house and steps will act as a slip sheet so when one moves slightly, one will not affect the other. If there is any concern of wicking it will remedy that as well.

As a mention, all masonry products soak up moisture, some less than others, but all do. Any masonry that is exposed to the weather is supposed to be rated to withstand this exposure and any wood in contact with the masonry, is to be pressure treated, at least in modern times. If it is an older home, it may not have pressure treated material and hopefully other means were used at the time to provide separation between the wood and masonry, whether it be a type of metal or even tar paper...

  • thank you, I've added a picture of what foundations look like and the concrete base of my project. Would this help you revise your answer?
    – kacpr
    Commented May 16, 2021 at 16:07
  • Are the brick walls 8" thick or a brick veneer over wood framing above the foundation? This will help in figuring whether you need that "buffer" between the steps and wall or not. Right now I believe you can set everything tight to the existing wall, with perhaps no more than a thin layer of plastic trimmed to the edges of the steps, and that is at the most...
    – Jack
    Commented May 16, 2021 at 16:15
  • What is the raised ledge that the new brick are setting on? It looks like the step would need to go up on that to maintain symmetry...
    – Jack
    Commented May 16, 2021 at 16:17
  • What they do in UK is put a layer of bricks, leave a small cavity for the air, then insulation and finally a block, I wouldn't know what it looks like under the ground level but I'd wager it's something like this - link
    – kacpr
    Commented May 16, 2021 at 16:20
  • The ledge on the right side of the picture? It's just some concrete, there is a brick construction (you can barely see it behind black pipe) between me and the neighbours, I wouldn't touch it, maybe just smooth it out, my wife wanted to put some planters on it
    – kacpr
    Commented May 16, 2021 at 16:24

I guess this is what you are intended to do. The suggestions indicated in the photo shall be adequate to prevent problems due to collecting water and moisture. Note the 12" x 12" trench is purposed for the free draining of water captured below the concrete pad. It should be filled with 6"-8" gravel and sandy materials, then overtopped by topsoil and grass. It means minimizing the potential of frost heave along the edges of the concrete pad.

The concrete pad to wall joint shall be sealed with a flexible sealant.

enter image description here

  • what would you suggest I use to fill the construction with? are the "aerated blocks" + concrete fine to use?
    – kacpr
    Commented May 18, 2021 at 9:59
  • That's fine. You only need something to fill the voids.
    – r13
    Commented May 18, 2021 at 12:01

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