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Hello,

I am looking to better insulate my parent’s 1970’s chalet bungalow as the upstairs is noticeably warmer than the downstairs. The upstairs also gets very hot in summer and cold at night and the living room downstairs can be very cold in the winter. The living room has large windows and two and a half of the walls are exterior walls, but I hope insulating above will help it retain more heat. I’m not in a position to be redecorating apart from perhaps removing part of the ceiling in the hallway cupboards, to gain access to the flat roof to push insulation into it.



There is cavity wall insulation and what appears to be the original fibreglass. The fibreglass, (shown in green), is about 60mm thick. The loft insulation is patchy in places and on the angled roof sections it is pushed up against the roofing felt and has no air gap at either the bottom where it meets the bricks or the top where it reaches the loft. At the top of the angled section near the loft, the fibreglass has turned black, presumably due to moisture making its way from the crawl space up into the loft. I can't see any evidence of mould or moisture on the joists.





Both the loft and crawl spaces are used for storage. There is airflow inside the crawl space coming from behind a row of bricks where the soffit is out of view. The crawl spaces have bits of plastic sheet and old carpet nailed against the angled roof to reduce the dust coming from the fibreglass. The gap along the roof between the crawl space and the loft (shown in yellow) is 85mm at its narrowest due to battens used to attach plasterboard and is currently stuffed full of fibreglass with no airflow gap.





I plan to add more insulation on the loft floor (shown in light blue), insulate behind the knee walls (red), the gap below the knee wall to stop drafts under the floor and downstairs light fittings (pink), the crawl space floor and downstairs flat roof (purple), the gap between crawl space and loft, leaving an airflow gap between the roofing felt (yellow), and possibly the rest of the living room ceiling (orange) by pushing insulation into it from the crawlspace.



Regarding the pink areas, once this has effectively been sealed with insulation stuffed into it, the orange area will no longer benefit from airflow from the crawl spaces. Will moisture from the kitchen and bathroom downstairs be able to pass through this area without collecting and rotting the floor joists? The upstairs has chipboard floorboards with one bedroom having laminate flooring and the other and the toilet a single piece of vinyl flooring each.

I’m not sure what type of insulation I should use for each area. My understanding is that the rigid foam board type is tricky to fit in between joists and the inevitable gaps will affect the insulation properties. Please let me know if my plan meets the principles of insulation and which types of insulation to use in each area.

Hi theteaboy,

Thank you for such a detailed post.
The easiest and most effective solution would be:
1. Increase the depth of the insulation in the purple crawl areas to the recommended 270mm if you wish to retain these areas for storage you may have to use 100mm PIR insulation and overboard this.
2. Plug the pink areas so the floor to ceiling cavity is this is effectively sealed.
3. Fit vent tiles into the roof either side of the loft and crawl space areas
4. Line the vertical walls, sloping walls and ceiling in the loft room with PIR backed plasterboard, replaster room.
You indicate that you do want to do redecorating so a less effective solution would be to carry out 1– 3 and then increase the insulation in the loft to 270 m.
Regards S

Thanks for your response. Unfortunately it looks as though I will have to carry out the work without interfering with the plasterboard.

stoneyboy wrote: ↑

Tue May 21, 2024 12:15 am

1. Increase the depth of the insulation in the purple crawl areas to the recommended 270mm if you wish to retain these areas for storage you may have to use 100mm PIR insulation and overboard this.

I recently laid OSB board on the floor in this area. Due to cables and junction boxes attached to the bottom of the vertical wall (red) and also central heating pipes opposite I think any over-boarding may end up with substantial gaps to avoid these objects. It’s certainly given me something to think about.

Is there anything I need to consider when insulating around mains and lighting cables and junction boxes (purple area?) One section looks like this:


and a few other areas have just one or two cables tacked to the floor joist.

stoneyboy wrote: ↑

Tue May 21, 2024 12:15 am

2. Plug the pink areas so the floor to ceiling cavity is this is effectively sealed.

When this is sealed I’m concerned that moisture rising particularly from the kitchen and bathroom which are both down stairs will end up in this area without the ventilation it once had from the crawlspace. Will moisture continue rising through the upstairs bedroom flooring? Both bedrooms have chipboard floor boards. One of the bedrooms has laminate flooring and the other a single piece of vinyl.

stoneyboy wrote: ↑

Tue May 21, 2024 12:15 am

3. Fit vent tiles into the roof either side of the loft and crawl space areas

Does ventilation become more critical when more insulation is added? If I remove all the original insulation (green) which is currently pushed up against the roofing felt, could I add something like a Felt Lap Vent? Without the original insulation on the angled part of the crawlspace I assume I need to make sure all exposed water pipes in the crawl space are adequately insulated?

stoneyboy wrote: ↑

Tue May 21, 2024 12:15 am

You indicate that you do want to do redecorating so a less effective solution would be to carry out 1– 3 and then increase the insulation in the loft to 270 m.

I will be addressing the loft floor boarding to increase loft insulation underneath as I understand it makes the most significant difference to heating bills. With more insulation preventing heat entering the loft, will this reduce the temperature in the loft to a degree that it will lessen the likelihood of condensation on the roofing felt?

Hi theteaboy,
As you are finding it is difficult to upgrade the insulation in a chalet bungalow without a complete roof strip and upgrade.
Point 1
It looks like you have 150/175 deep joists in the purple crawl areas, lift the boarding you already have in place, add 100/125 packers, fill the gaps between the joists completely and relay the boarding. Fit the insulation over any pipes. In an ideal world all cables encased in insulation should be down rated in line with the Regs, if you have cables carry close to their rated capacity you could relocate them above any insulation. Seek professional help if you have any doubts.
Point 2
Yes moisture in the vapour phase will rise into the crawl areas (where ventilation will remove it) and through the loft room into the loft (again where ventilation will remove it)
Point 3
There is little point in removing the insulation in the green areas. You will have difficulty removing the insulation in the yellow areas which is why I suggested overboarding with PIR backed insulation board (go over the existing plasterboard)

Increasing the depth of insulation will increase the likelihood of condensation forming which is why ventilation is so important. Ventilating the crawl and loft areas should reduce the chance of condensation forming in the yellow areas.

How we live in our homes will dictate condensation levels, if we have an airtight house with no trickle vents, never open windows, dry clothes indoors, cook in saucepans with no extraction, use showers again with no extraction and have minimal heating the likelihood of condensation problems is increased.

With a retrofit insulation job it may be suck it and see to determine what works.

Regards S

...lift the boarding you already have in place, add 100/125 packers, fill the gaps between the joists completely and relay the boarding.

I'm not sure what you mean by packers?

Yes moisture in the vapour phase will rise into the crawl areas (where ventilation will remove it) and through the loft room into the loft (again where ventilation will remove it)

Okay, good. I just wanted to make sure I wasn't trapping moisture in the floor/ceiling void where I wouldn't be able to see it after effectively sealing it.

You will have difficulty removing the insulation in the yellow areas which is why I suggested overboarding with PIR backed insulation board (go over the existing plasterboard)

I have access to the top and bottom of the yellow area. If I remove the fibreglass from this area only, I think I can slide some PIR into it from the loft.

Increasing the depth of insulation will increase the likelihood of condensation forming which is why ventilation is so important. Ventilating the crawl and loft areas should reduce the chance of condensation forming in the yellow areas.

Are vented tiles a lot more effective than the Felt Lap Vents?

Hi theteaboy,
To increase the depth of the existing joists you could fit bits of 125x50 on top of them or you could use a number of short pieces (packers), the advantage of the short pieces is that you can work round existing services on top of the joists.
Even if you could remove the glass fibre in the yellow areas you will have great difficulty in fitting PIR boarding in their place - joists are never perfectly parallel and there will be other obstruction to hinder you eg skewed nails. It is inevitable that you will end up with gaps between the boards and rafters - this cold bridge will result in cold bands down the loft room sloping ceilings with condensation and mould forming as strips.
If you use vent tiles you might get away with removing one tile for each vent tile. Presumably the underslaters felt is the tar/hemp type, this goes brittle in time so try one felt lap vent and see if it works without splitting the felt.
Regards S

I managed to remove the glass-fibre from one section in the yellow area, by pulling it up into the loft. I think I could push up a 70mm Rockwool insulation slab (or similar) from the crawl space into the yellow area, leaving a 50mm airflow gap above where cables can be laid on top. I think I would need to cut two slits in the slab for the two battens in that area to sit in. Are the slabs likely dense enough to be pushed up in this manner?

I think the rest of the glass fibre (angled green section) as well as the old carpet nailed against it to reduce the dust coming from it will need to be removed to improve air flow in the crawl space. I assume after removing this, the crawl space will get hotter in the summer and colder in winter? Is there any specific insulation you would recommend for pipes considering most of the pipes run two side by side, therefore not allowing for traditional pipe lagging.

Hi theteaboy,
Assuming you will be fitting RWA46 this should be stiff enough to push in place but the slabs vary in stiffness so it may be a trial and error process.
Assuming the pipes are laid above the joists, take your loft insulation strips over the pipes - do not insulate under them.
Regards S

Thanks for the suggestion. It looks as though RWA45 is available only in 600mm widths. As my joists are 370mm apart this is no good. Are there any specific types of material that would be suitable for that area? Is the density of the material relevant?

I am considering PIR board with Gapo-Tape for the red areas (knee wall). However I have noticed many nails in the joists that are sticking out (see photo). Should I try and knock these in further or leave them alone? Would these interfere with Gapo-Tape?

Hi theteaboy,
I don’t know of any insulation that comes in 350mm widths If you are going to use REA45 best to cut this into 350mm strips across the slabs leaving a narrow piece of waste. I find a sharp carving knife very effective at cutting the slabs.
The nail heads will be inconvenient for fitting rigid insulation panels, if you try to drive them home you will probably end up splitting the studs it’s worth a try but use a heavy punch and hammer. You could also try driving the nails horizontally into the studs, hold a club hammer on one side of the stud and hit the opposite side with a hammer to see if you can sink the heads flat.
Regards S