Internal solid wall and floor insulation advice

[jimmy rivers]

Hi Folks of the UKW,

We’ve recently moved into an old property (200 yrs approx) which is of a solid wall construction and I'm looking for a little advice as to the best route to do some remedial insulation to our downstairs lounge walls and floor.

The previous owners membraned the inside of the solid walls and plasterboarded over a 2x2 stud work frame. The floors are a 5x1 T&G softwood board over 4x3 floor joists (no noggins) I know this as there is a small 2m sq pit underneath a part of the floor which is accessed via a trapdoor. The finish is great and the floor is nicely laid, however there is zero, zilch, nada insulation in the room and I can already tell that this is going to be a very cold room come winter :?

My experiences are more with Cabinet & Furniture Making so I would be grateful for any advice from those in the know on the most appropriate approach to tackle this project and the common pit falls... especially regarding... addition moisture membranes, working around windows and doorways to avoid condensation from cold spots and rotting studs/ floor joists

After plenty of Googling my initial considerations are:-

Part A:- Remove the fixtures (rads etc) and skirting before lifting the floor to slip Kingspan in-between the joists on battens(?). The joists are on bricks and slate packers approximately 3-4 inches off the dirt and I can see air bricks to the front of the house, so air circulation should be good.


Part B:- After the floor I would move onto the walls by either boarding over with insulated backed plasterboard (77mm) OR ripping off ALL the plaster boarding to insulate between the existing 2x2 studs (50mm) Kingsapn before re-boarding and skimming.

The Energy Saving Trust website suggests that I need to achieve a U value of no more than 30 W/m2k with regards to meeting regulations but I’m not sure if this is achievable with 50mm Kingspan?

I’ve attached a plan view of the layout and an (approx) exploded elevation to show the construction methods of the room at present.

All in all I sense it’s going to be a messy job and I am cursing the previous owners for not insulating when they had the chance! (hammer)


Thanks in advance,

Jim

 

[PAC1]

Two questions:
Are there any signs of damp inside?
Could you insulate from the outside by fixing insulation then rendering to the outside?

You might be able to get a grant for some of this work from a Government scheme for energy efficiency.

 

[jimmy_s]

You would struggle to get a U value of 0.3w/sqmk with 50mm kingspan I would think - unless the walls are very thick.

If there is a membrane on the wall you might need to remove it as any vapour membrane should be on the warm side of the insulation as if its in the wrong place you can end up with interstitial condensation.

You could use mineral wool quilt on nets in the floor instead of kingspan - might be easier to install tight between the joists.

 

[jimmy rivers]

Thank you for the replies.

PAC - Currently everything is nice and dry inside.

We looked into grants but found them to be best suited to cavity wall, exterior render or treatment of all the internal rooms in one hit which would of been too expensive /disruptive for us

Rendering the outside would unfortunately change the appearance / character of the property and probably upset our semi detached neighbour.

The EST suggests a DIY 'room-as-you-go' approach when upgrades take place such as...new kitchens, bathrooms, decorating for example.

But I may of missed an alternative source, any leads very much appreciated.

Jimmy - I did wonder about the position of the membrane, so more like this with the membrane on top?




Cheers Jim

 

[jimmy_s]

Hi Jimmy

Yes - normally that's where it would go if you put it on the cold side then it can cause vapour to condense in the middle of the wall construction. The kingspan and plasterboard will prob be foil faced so you shouldn't need a separate vapour membrane.

 

[dickm]

Can't be sure from your diagram, but could you get access (however uncomfortable!!) to the underside of the floor? If you could crawl into the space, then fibreglass or any other form of insulation between the floor joists, held in place with some sort of netting stapled to the underside of the joists, would work fine. Would save the upheaval of raising the floor.
Son-in-law has just insulated the floor in their house using fibreglass plus net and it makes an enormous difference.

 

[jimmy rivers]

Hi dickm . . . unfortunately the clearance for 80% of the floor is about 3-4" under the joists. Definitely considering hanging some fibreglass off netting once the floor is up, another option (for SWIMBO to consider) might be a carpet with an insulation grade underlay.

The kingspan and plasterboard will prob be foil faced so you shouldn't need a separate vapour membrane.

Probably a daft question (led by the paranoia of damp) but. . . without a vapour barrier, is a tight fit between the studwork all that is required or would I need to seal around the KS panels ?

Cheers,

Jim

 

[RobinBHM]

Regarding the wall insulation, I think the preferred method is to cover the wall with the insulation (in this case 50mm) with no gaps, and screw 50 x 20mm battens onto the insulation, laid flat. That way there are no stud thermal bridges. Any gaps can be foamed.

It also means there is no studwork touching the cold wall where condensation may form. If you tape all of the foil faced insulation before attaching the battens this will act as a vapour barrier. You could then use foil backed plaster board or a vapour barrier as a belt and braces approach. Battens need to be at plasterboard spacings.

I'm never sure about foil backed plasterboard since it is pretty difficult to tape each joint effectively, as it is at the back -perhaps somebody has an idea how this is done.

When Ive done this work, Ive used 75mm wide hardwood battens where radiators will be hung.

Small retaining battens on the floor joists and resting the insulation on them works well. Of course cutting insulation in between floor joists is not an exact science since they are likely to have varying gaps and often bowed. The gaps can be foamed, cut off when dry and silver tape applied spanning the joists.

Cheers Robin

 

[alunt]

I moved into my current home in 2010 just before the -18 Degrees winter.
After spending £300 every 6 weeks on LPG heating i decided to rip out all the walls in the Lounge, replace them with 3x2 CLS 50mm Kingspan/Celotex and tapered edge plasterboard (12.5mm on the walls, 9mm on the ceiling). No vapor barrier.
As long as your posts don't touch the outside walls and you have plenty air circulating between the stonework and the kingspan then moisture wont be an issue.
I hammered nails into the posts to prevent the kingspan falling back against the stone walls.

I crawled under the floor with 100mm glass wool and netting stapled up to the joists.
I doubled up the glass wool in the loft.
I then nailed down 4mm plywood on the floor to prevent drafts coming up through the floorboards.

This made such a difference that i have since performed the same procedure on the bedrooms and the Kitchen.

I probably only spend £300/year on LPG now. The bulk of the heat coming from the Log Burner (I get 4 tons of tree end cuts from my local sawmill for £105 which i cut up with a chainsaw. This does the whole winter easy).