Porch conversion

[NoPaddle]

We are hoping to convert an external porch to an internal porch with downstairs toilet.

 

The existing porch has brick columns shown in the image below that contribute to the properties charater and so I'd like to leave them in place and exposed externally.

 

 

What is the best way to deal with the insulation where the columns are, and what about penetrating and possible rising damp? I've started to sketch the design as shown below.

 

 

Thoughts and advice backed with evidence and experience would be very welcome.

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[DevilDamo]

Brick external skin with a DPC and an insulated timber frame internally.

[NoPaddle]

Thanks for the reply. I have changed the design a bit to fit within permitted development size requirements. To maximise the internal space, It would be better if I could avoid having the inner leaf run around the inside of the pillar.

 

To avoid a thermal bridge, I will add some sort of insulation offset from the pillar, shown above in purple. What are my options here? I realise the thickness shown might be a bit optimistic to maintain an acceptable heat transfer.

 

Also, should I drill and inject a damp-proofing cream into the mortar on the pillars, or would that come with its own problems?

 

[Nickfromwales]

You should be insulating the slab somehow too, assuming you’ll put a radiator out there. So I also assume you’ll know you’ll need to dig the pathway up to install footings for the brick walls? A new slab will be needed with insulation and DPM to form the floor.

 

Insulation needs to go against the brickwork, so use Marmox boards (minimum 40mm) to clad those, stopping short of where the cavity gets closed by the external

leaf of new brickwork. Then drill and fix the timber studs / frames to that, using foam and fixings.

 

You'll need to fit DPC everywhere to stave off any future damp issues.

 

Not contacting the pillar would be best, as per your previous. 

[Nickfromwales]

Why PD? Why not go for the original design if a downstairs additional WC is required / of long term benefit? 
 

A planning application isn’t likely to fail here imo.

[NoPaddle]

Thanks Nick,

This is part of a larger extension project, and I wanted to submit plans to get a lawful development certificate. However, you make a good point about standing a good chance with successful planning with the porch - I could apply for planning for this accept separately after the PD certificate has been issued.

 

(I've decided to move the WC to a small room that we already have inside the house, but a bigger enclosed porch would give us more utility space.)

 

There will be some sort of heating. I've not figured out the floor construction yet. It is currently tiled and I am not sure how thick the concrete is underneath, but I was assuming it would need new footings.

 

 

 

 

I will look into Marmox boards.

[Nickfromwales]

1 hour ago, NoPaddle said:

Thanks Nick,

This is part of a larger extension project, and I wanted to submit plans to get a lawful development certificate. However, you make a good point about standing a good chance with successful planning with the porch - I could apply for planning for this accept separately after the PD certificate has been issued.

 

(I've decided to move the WC to a small room that we already have inside the house, but a bigger enclosed porch would give us more utility space.)

 

There will be some sort of heating. I've not figured out the floor construction yet. It is currently tiled and I am not sure how thick the concrete is underneath, but I was assuming it would need new footings.

 

 

 

 

I will look into Marmox boards.

Defo a new slab and footings, as b regs will not allow space heating in non-insulated spaces due to terrible energy losses. You're not even supposed to put a radiator in conservatory as they have open ventilated ridge details.

 

You could sample the slab and see if it's robust, and if so you could just bond PIR to it and build up to the level of the doorway, less the thickness of the floor covering, but in honesty once you disturb this for footings there will not be much worth salvaging.

 

Better to lift the footings and lay the slab so you step up into the new porch, to weatherproof it, giving ample opportunity to insulate and then heat it with less losses.

[NoPaddle]

That approach makes sense. Thank you.