Boarding: Ceilings - Insulation

Previously we had laid the floor in the 'attic room'. Now with all the ceilings fitted in place, we needed to go back to the attic and lay the loft insulation.

Modern building regs call for very deep layers of loft insulation - which is fine for most of the attic but can cause problems (especially with the local building inspectors) if you lay flooring in certain areas as we had.

One common solution is to simply raise the floor level so that you can fit all the insulation underneath, but that would mean losing all the headroom in the attic. Alternatively, we could use a much denser PIR type insulation, like Celotex, underneath the attic floor, but this in turn would throw up a whole host of problems relating to the downlighters we would be fitting in the upstairs ceilings, not to mention the expense.
 




The solution for us was to use a mixture of both; a layer of mineral wool followed by a layer of Celotex. Alan calculated all the u-values online to work out the exact thicknesses we would need. He also got the insulation manufacturers to send over an authorised specification to prove to our building inspectors that it would match the same insulation figures as everywhere else.

We fitted the insulation under the attic floor in sections. The plasterboard ceiling is underneath the green plastic vapour barrier.

In order to simplify the fitting of the ceiling downlights, the lower level of our insulated filling would be Rockwool. Much denser and more thermally efficient than conventional loft roll, Rockwool was also a good deal cheaper than Celotex.

The Rockwool comes in thick slabs designed to fit perfectly between the joists so fitting them consisted of squidging them neatly into place.

While I got on with the job of fitting the Rockwool slabs, Alan was in the room below swearing at cutting sections of Celotex for the next layer.

Once the Rockwool was in, I could start fitting the Celotex - you can see the first section cut to size and ready for me to fit. As the Celotex is rigid, getting it to fit snugly meant a lot of trimming and adjusting.

The Celotex is much more thermally efficient than the Rockwool and was needed to get the u-value (which is just the measure for how well a material insulates) to the required level. We'd have liked to have just used Rockwool alone but even if we'd filled the underfloor space to the brim with the densest slab available, we'd still fall way short of the u-value we needed, so had to use Celotex to make up the shortfall.    

Next section of the attic floor.

The final section is completed and ready to be covered by the OSB floor once again. With horrible dust from both the mineral wool and the Celotex filling the attic, a decent face mask proved a wise investment.

Once the attic floor had been insulated, we could get started on the simpler task of insulating the rest of the loft. The cheapest and most efficient method is still to use standard loft roll, though our building specification called for rather a lot of it.

We started off with a thick layer running between the joists.

This is where those rafter trays we fitted proved their worth. We could squash loft roll right up to the edges above the walls without blocking the roof ventilation.

After filling all the available space between the rafters, we laid another thick layer of loft roll crosswise over the top. This really improves the thermal efficiency by helping to stop cold bridging.

We cut smaller sections for the bits right under the eaves and once again squashed them tightly up against the rafter trays.

Then the second layer of loft roll was laid sideways across all the joists.

Same treatment on the other side. These modern building regs certainly like their insulation - that loft roll is almost half a metre thick!

Next we needed to fit the ceilings downstairs. Unlike the rooms upstairs, these don't need any thermal insulation (because any heat escaping from the ground floor just rises to the first floor instead of being lost to a cold attic) but building regulations do require acoustic insulation to prevent transmission of noise between the floors.

Our floor construction, which included a dry cement screed laid upstairs, was probably already soundproof enough to pass regulations, but since we were building the house for our own use, it made sense for us to add extra acoustic insulation before the ceilings went on to really help block out any noise between the floors.

Before filling the ceiling void with acoustic insulation, we ran all the wiring for the computers, phones, TV aerials, etc. Unlike electrical wiring, audio visual wiring does not need to be certified by an electrician so we could save money by doing it all ourselves. Alan drew up a wiring plan and we started threading yet more cables up and around the joists.

The upstairs cupboard will house the junction box for all the TV aerial feeds so all the cables were sent there...

We tried to route all the audio visual cable well away from electrical cables to avoid any possible interference.

Once again, the metal web joists made the job of threading all the cabling between rooms much easier, though we still had to be very careful to avoid all the pipes, ducts and electrical wiring when drilling any holes through the floor.

Computer and phone cabling terminates in what will be the study. Although cordless phones and wi-fi computer networks are pretty good nowadays, hard cabling still has many advantages (especially as our whole house is sheathed inside and out with a silver foil breather membrane that can really mess up wireless signals!)

We made a last minute decision to run wiring for surround sound speakers in the lounge. The cost was minimal as we had plenty of spare cable and obviously it's much easier to do it now before any walls or ceilings are up.

Cutting holes for the back boxes that will feed each of the seven speakers.

The sockets behind the TV are getting rather busy.

While Alan finished off the audio cabling, I insulated the area under the porch roof in the entrance hall using Celotex and loft roll.

Once all the audio visual cabling was completed, we could insulate the ceilings. The loft roll that we had used up in the attic works well to prevent heat from escaping, but really doesn't do much as a soundproofing material (the manufacturers don't even publish any figures for its acoustic performance). Although it looks much the same as the loft roll, the acoustic roll is very different and is rated specifically to deaden sound.

With no access to the space above the ceiling once it is boarded, the only way to fit the insulation is to get it in place before the boards go up. It's not rigid enough to stay up on its own so I suspended it between the joists using string lines.

One row of soundproofing installed in the lounge.

Completing the insulation for the hallway.

The site manager came to check I was fitting it all correctly.

Utility room and WC completed.

The kitchen and dining area was a long slog.

The study.

The lounge completed.

The site inspector kindly conducted a physical demonstration on how to fit insulation into a small space. We couldn't have managed the job without his help and sage advice.