Insulate a lean to

[Nauticool]

Hi

I have a lean to next to my lounge that I wish to start using as a dinning room. It will be heated via a rad from existing loop.
The room is 8m x 4m.
The build is of single brick but double glazed windows and doors.
Can anyone give me a bit of guidance on how to insulate this area?
I was thinking for walls membrane then attach stud work to wall and infill with cellotex.
Then for ceiling cellotex in between joists then board and plaster.
Am I heading in the right direction?

Many thanks in advance

Glenn

 

[freddiemercurystwin]

Walls: brickwork, assuming well pointed, coated internally with min. 2 layers of RIW flexiseal with 25x50 vertical treated s/w battens @ max. 600 centres to form air gap and services void fixed to brickwork with additional layer of dpm behind each batten, affix 75mm rigid Celotex pl4000 foil backed insulation (or Kingspan or other PiR insulation), (tape all joints with foil tape) and 1 layer 12.5mm wallboard and skimmed. Fit some thin insulated plasterboard to the reveals to maintain insulation up to the windows.

Roof: fit 140mm rigid insulation between the rafters so that there is no air gap between the flat roof deck and the insulation. Foil backed plasterboard + skim to form the ceiling.

Floor: don't know as you've not said what the existing is (concrete or suspended timber) or whether the floor is flush with the main house or there is a step down.

 

[Nauticool]

Walls: brickwork, assuming well pointed, coated internally with min. 2 layers of RIW flexiseal with 25x50 vertical treated s/w battens @ max. 600 centres to form air gap and services void fixed to brickwork with additional layer of dpm behind each batten, affix 75mm rigid Celotex pl4000 foil backed insulation (or Kingspan or other PiR insulation), (tape all joints with foil tape) and 1 layer 12.5mm wallboard and skimmed. Fit some thin insulated plasterboard to the reveals to maintain insulation up to the windows.

Roof: fit 140mm rigid insulation between the rafters so that there is no air gap between the flat roof deck and the insulation. Foil backed plasterboard + skim to form the ceiling.

Floor: don't know as you've not said what the existing is (concrete or suspended timber) or whether the floor is flush with the main house or there is a step down.

Thanks for that!

You do step down onto the concrete floor but it is raised by about 50mm off the outside ground level, not sure what's underneath it

I assume I won't be needing ventilation, air bricks, on the wall as I am not creating a cavity?

 

[Nauticool]

Walls: brickwork, assuming well pointed, coated internally with min. 2 layers of RIW flexiseal with 25x50 vertical treated s/w battens @ max. 600 centres to form air gap and services void fixed to brickwork with additional layer of dpm behind each batten, affix 75mm rigid Celotex pl4000 foil backed insulation (or Kingspan or other PiR insulation), (tape all joints with foil tape) and 1 layer 12.5mm wallboard and skimmed. Fit some thin insulated plasterboard to the reveals to maintain insulation up to the windows.

Roof: fit 140mm rigid insulation between the rafters so that there is no air gap between the flat roof deck and the insulation. Foil backed plasterboard + skim to form the ceiling.

Floor: don't know as you've not said what the existing is (concrete or suspended timber) or whether the floor is flush with the main house or there is a step down.

Thanks for that!

You do step down onto the concrete floor but it is raised by about 50mm off the outside ground level, not sure what's underneath it

I assume I won't be needing ventilation, air bricks, on the wall as I am not creating a cavity?

Oops my bad, there is an air gap so will it need ventilation?

 

[freddiemercurystwin]

No need for ventilation in the walls, cavities in cavity walls do not need ventilating anyway. A trickle vent in the window is a good idea (mandatory under Building Regs) if you are fitting a new window though. Consider retrofitting a trickle vent in the window if it does not have one.

For the floor, you would lay down a dpm, add battens with insulation between the board on top. the insulation thickness/batten height being the variables to get you a flush floor level.

 

[joe-90]

Freddie, I've saved that post as reference. Btw, do you know how you would go about calculating the 'u' value on the finished room?

 

[Nauticool]

No need for ventilation in the walls, cavities in cavity walls do not need ventilating anyway. A trickle vent in the window is a good idea (mandatory under Building Regs) if you are fitting a new window though. Consider retrofitting a trickle vent in the window if it does not have one.

For the floor, you would lay down a dpm, add battens with insulation between the board on top. the insulation thickness/batten height being the variables to get you a flush floor level.

There is already Dpm underneath the concrete floor should I still lay some before insulation?

Builder has told me to fill the air gap with cellotex and not have one but not sure why. Which is best air gap or none?

Also I will have a 50mm air gap between insulation and roof due to the way the joists are fitted. Should I vent this to avoid sweating?

Thanks again, great site!

 

[freddiemercurystwin]

No need for an additional dpm if there is already an effective one under the slab.

You can do the walls with an air gap or without one it makes no odds. Many on here do not bother. There are several different approaches to this.

Why do you have a void in your roof? If you must have a gap then yes you will need to ventilate this at each end of the joists.

 

[freddiemercurystwin]

Freddie, I've saved that post as reference. Btw, do you know how you would go about calculating the 'u' value on the finished room?

In the first instance I'd be on the Celotex U Value calculator, you do have to register to use it but that's no fuss. The calculator allows you to calculate most domestic situations. Anything more complicated I'd get on the blower. There are other U Value calculators but none are as simple as the Celotex one.

There's no such thing as a U Value for the room only a type construction ie a wall, floor or roof etc.

 

[Nauticool]

Walls: brickwork, assuming well pointed, coated internally with min. 2 layers of RIW flexiseal with 25x50 vertical treated s/w battens @ max. 600 centres to form air gap and services void fixed to brickwork with additional layer of dpm behind each batten, affix 75mm rigid Celotex pl4000 foil backed insulation (or Kingspan or other PiR insulation), (tape all joints with foil tape) and 1 layer 12.5mm wallboard and skimmed. Fit some thin insulated plasterboard to the reveals to maintain insulation up to the windows.

There is an effective damp course which ends up 100mm above the internal slab. Am I right in saying I shouldn't build my floor above this?
Also will I still need the riw flexiseal as there is damp course present?
If so is there a similar product as no one seems to sell it around Bournemouth area

 

[joe-90]

This stuff is cheap and popular.

http://compare.ebay.co.uk/like/150686940851?var=lv&ltyp=AllFixedPriceItemTypes&var=sbar

 

[freddiemercurystwin]

There is an effective damp course which ends up 100mm above the internal slab. Am I right in saying I shouldn't build my floor above this?
Also will I still need the riw flexiseal as there is damp course present?
If so is there a similar product as no one seems to sell it around Bournemouth area

You can build your internal floor where you like. Take the RIW or the stuff Joe suggested down the wall to meet the existing slab. The RIW is to stop any damp penetrating through the wall.