Isolating the southern knee wall in music room

The southern wall stands next to a partial poured concrete wall. The attachment point for WIC clips is 16" below  the top of the wall. At this height the two walls would be around 8" apart due to the concrete wall below. To bridge the gap I used 2x4 pieces, attached to the inner wall with 3 x 2.5" screws.

This wall was pre-built on the ground, without the studs that would connect to WIC. This allowed me to insert these studs after the wall was standing and I could line up the inner studs.

Isolating the support beam

I decided to use single leg resilient channel (RC1) to isolate the support structure that was mentioned in an earlier post. I have built the adjacent walls so that they are flush with the surface of the RC1.

RC1 provides acceptable sound isolation at an extremely cheap price, and without using up a lot of space.

North side wall of studio room complete

I wanted to try using RC2 (double leg resilient channel) to secure the soffit frame to the joists, but found it hard to find RC2 locally, so I stuck with the more expensive RSIC-DC04 option used in the home theatre. Overall this wall was similar to the adjacent home theatre wall.

Click here to see photos of the wall construction

Up next, the simpler south side walls.

Double stud walls

One of the most effective ways to isolate a room is to build a second wall; a room within a room. Most importantly, the inner walls/ceiling should limit sound transfer through separation from the outer walls.

I have chosen to build second stud walls on all walls except the wall between the recording room and home theatre and one exterior wall (more on that when I start work on that wall).

Most walls will be attached to each other with WIC clips from Mason Industries (pictured below). For most of my walls, placing these clips at 8ft centres will suffice, with one clip at each end of a wall. I built the walls on the ground first (longest being 16ft), stood them up, beaded the bottom plate with soundproofing caulk, fastened the bottom plate to the concrete with red head bolts and powder driven nails. Then I attached the WICs to each wall with 1 inch lag screws, making sure the new wall was standing square.

I have built a soffit around the HVAC ducts. The underside of the soffit connects to the inner wall directly (with wood screws). The top plate of the soffit connects to the joists with RSIC-DC04 brackets (2ft on centre) to ensure sound transfer to the floor above is minimised.

I did run into a problem with the WICs for some of the walls. There was tension pulling the two joined walls together, which caused the WIC to slip (the glue did not hold). Since these clips are used in music halls and tv studios, I assume it is not a flaw in the clip, but that they are not meant to handle this kind of strain. To prevent the walls pulling together, I used RSIC-DC04s mounted on the inner wall, as a buffer (I wonder how this problem is dealt with in commercial construction).

The wall between home theatre and music room

Although the home builder put a wall to separate the HT and music room, I had to pull it down, as it wasn't isolated from the ceiling. I am not concerned about noise transmission between the two rooms (it is highly unlikely both rooms will be used at once). I do want to prevent sound from traveling up the wall, onto the joists and throughout the rest of the house.

I decided to use RSIC-DC04 isolation clips from soundisolationstore.com to attach the top plate of the wall to the joists - at 2' OC (manufacturers recommendation). This totaled about 7 clips for the whole wall.

This was my first time using these clips, so I learnt some lessons for next time. Here was my technique: 1) Attach clips to top plate on the floor - screw through center of waffle. 2) Attach top plate to joists with screws through metal part of clip. 3) Build base plate, and finish the wall with studs etc.

The problem with this technique was that the RSIC clips were fixed before the studs were built. So after I put the studs in, the pressure on the top plate was different to when I fastened the top plate - creating tension on the clips. This probably doesn't optimize the effectiveness of the clip, but is not a big deal.

 

 

Structural reinforcement

Due to the additional weight being added to the ceiling (already 3 layers of 5/8" drywall under the subfloor, and 2 layers on the ceiling), it was necessary to determine that the joists could support the mass. My builder did some calculations, and although it seemed safe, decided to build a support beam under the joists that were 2' longer than the rest of the joists - to be sure.

As seen in the photo below, this support beam and posts are not isolated from the structure (wouldn't be a support beam otherwise!). Therefore, some work will be required to separate the drywall and the support structure in the future.

Insulating concrete walls

Building Science.com contains many of the most recent advancements in building techniques. It even provides complete residential designs depending on which climate zone your house is located at.

My house is located in a mixed-humid climate, and one of the recommendations is to use foam insulation on bare concrete walls, with thickness of at least 1.5 inches (especially if this was not done on the outside of the house).

A money saving tip - using 2 layers of 3/4 inch foam is considerably cheaper than 1.5 inch foam. Apply foam such that no seams overlap. Use glue specifically for foamboard. On the final layer, tape seams with Tyvek tape.

Next, isolated framing and moisture sensors...

Completed adding more mass to basement ceiling

In my last post I mentioned a short cut for adding layers of sheetrock to the ceiling between the joists. Gervais recommends putting up one layer of sheetrock at a time, and apply foam backer rod with caulking around the gaps for each layer.

Instead, I cut the sheetrock so that the 3 layers were still joined by folding the sheetrock. This allowed for putting all 3 layers up at once. I then used spray foam to seal all the gaps. I ended up doing about half the work myself. Both the builders and I found it took about an hour to do each joist gap (about 14ft in length). With about 30 joists in total, this is a considerable time investment. If I had followed the exact technique described by Gervais, it would have taken at least 3 times as long.

In terms of physical work, it will easily be the most difficult task in completing my basement - and its complete!

Before:

After:

See photo gallery for more images.