Porch dpc and cavity questions

[DarrenPalfreyman]

hello everyone. Im looking for some advise. Ive lived in this house a couple of years now and boy did it need some work. My next project is to remove this upvc porch and replace it with double skin walls and a large front door with side windows. Ive asked if i need planning and as its a porch and im keeping an external door in the original place that its not needed. The base is a raft. I will be putting dpc along all bases to build up on but im unsure if i need a vertical dpc where it joins the existing building? I would like to plaster the internal walls along with rendering the external. Also should i use full cavity insulation or partial the cavity will be 75mm. Any advice would be greatly appreiated.

[Temp]

I'd either cut the house wall so the cavity is continuous or run a saw cut up and install a vertical DPC.

 

Fully filled cavities are Ok if you use insulation approved for that. Building Control may have a view.

 

 

 

[DarrenPalfreyman]

Thank you for your input. You think joining the cavity to existing wall and using partial insulation with cavity trays and weep holes would be my better option then

[DevilDamo]

Are you replacing the porch on a like for like basis, including its size? If so, how big is it as it looks to exceed 3sq.m in external footprint so Planning may actually come into to?

 

If you’re retaining the original front door, you’d be exempt from BR’s so can build and insulate it how you like. If you are going for a 75mm cavity (although 100mm is current regs for comparable purposes), you’d end up fully filling it. A partial fill cavity normally requires a 50mm clear cavity so would only have 25mm of rigid insulation. Partial filling is also a bit of a backward way of building a cavity wall and is something the majority of old school builders do not like.

[DarrenPalfreyman]

Yes it will be like for like its 3000mm wide and 1500mm deep.i will be keeping the original external door but will replace it later on once the porch is complete. Ok so i will go 100mm cavity anyway and fully fill the cavity with rockwool. Do i still need to join existing building cavity or fit a vertical dpc? I will have to phone my local planning then im just going of what ive been googling if i need regs or permission. 

[DevilDamo]

You’ll need Planning as it’ll exceed 3sq.m.

 

As mentioned, it will not require Building Regulations if you’re retaining the original front door.

 

Assuming the existing house is cavity, then it’s best practice to connect the new cavity to the existing along with physically lapping the new and existing external DPC’s.

[DarrenPalfreyman]

Brill Thanks for all your help