extra isolation planning for cavity wall and roof

Hey guys, i am gonna start planning some extra isolation for my build so that if i need more isolation at the end of the day i have it planned. I going to start with the cavity wall. My build consists of a cavity wall, single brick wall, air gap single brick wall, MAM system. if i would like to further improve isolation what would you suggest? seeing as it is already a two leaf system, adding a drywall frame on the rooms inside filled with wool and then sealed with drywall would turn it into a 3 leaf system..... so my thinking led me to the following idea. Please let me know what you think of my idea and also what would be the consequences of doing the 3 leaf design, would it honoustly not be worth it and would my idea be better as in the pic.

Preludetojune wrote:

Hey guys, i am gonna start planning some extra isolation for my build so that if i need more isolation at the end of the day i have it planned. I going to start with the cavity wall. My build consists of a cavity wall, single brick wall, air gap single brick wall, MAM system. if i would like to further improve isolation what would you suggest? seeing as it is already a two leaf system, adding a drywall frame on the rooms inside filled with wool and then sealed with drywall would turn it into a 3 leaf system..... so my thinking led me to the following idea.

Pre, I seriously doubt that it's a MAM system - the odds are the 2 wythes are tied together with mason ties. I say this because single wythe brick structures do not stand up very long. There is also going to be a whole lot of mortar in between the 2 wythes - which couple the walls even more. In addition - the 1" air space is almost a non-existent spring when it comes to a leaf as rigid as brick......... I would opt for the room within a room approach. All of that being said - loose the "softboard" it's a waste. If you want something between sheets buy green glue - if you can't afford greenglue on your budget then add another layer of drywall....... and make sure to use 5/8" drywall so as to maximize mass. Use 2x6 framing at 24" oc - with fluffy insulation in the bays - and a 1" space between the framing and the brick - that will give you a 6 1/2" air space - which is not fantastic - but is adequate. Sincerely, Rod Please let me know what you think of my idea and also what would be the consequences of doing the 3 leaf design, would it honoustly not be worth it and would my idea be better as in the pic.[/quote]

Why? It was discussed in this thread, complete with references to similar wall TL test results. Also in this thread. The attachment to this thread shows the amount of TL you can expect in the range of. Repeating, your weak link in isolation is the roof. After that it is that the two walls are coupled by the ground they are on. The IR 586 shows the effect of isolated foundations. Andre

Thanks for your replies, Rod and Andre, i respect both your oppinions. Andre i want to just make 100% certain before i make more problems for myself. Rod, the cavity walls have been connected through the usage of "brick force" at every +- 8 brick layers to reinforce the walls, im not sure if that is what you mean by "mortar ties" and yes there is some messed mortar that fell between the walls during construction. So are you saying that it is now really a one leaf system and i should treat it as a one leaf system?

Preludetojune wrote:

Thanks for your replies, Rod and Andre, i respect both your oppinions. Andre i want to just make 100% certain before i make more problems for myself. Rod, the cavity walls have been connected through the usage of "brick force" at every +- 8 brick layers to reinforce the walls, im not sure if that is what you mean by "mortar ties" and yes there is some messed mortar that fell between the walls during construction. So are you saying that it is now really a one leaf system and i should treat it as a one leaf system?

Yup - that's sure nuff what I am saying. Bonding Brick (what you describe your construction as) along with the mortar in the wall cavity will really make this act as a single leaf. When those tests were done in the IRC study - their projection for the double wythe masonry walls was in a perfect world - connections made only with metal brick ties - and no mortar in the cavity. Rod

Preludetojune wrote:

Rod, the cavity walls have been connected through the usage of "brick force" at every +- 8 brick layers to reinforce the walls,

Is this the "Brick Force" you are referring to?Can you show in a picture how it is used? Andre

rod gervais wrote:

When those tests were done in the BBC study - their projection for the double wythe masonry walls was in a perfect world - connections made only with metal brick ties - and no mortar in the cavity.

Which BBC study is this? I am not familiar with it. Cf my previous post for more information on the brick force. It may be metal ties between the wythes. I don't think the mortar in the cavity is significant because both wythes are on the same ground with no isolation. I may be wrong, and it won't be first time, or the last. :) Honestly, Andre

AVare wrote:

rod gervais wrote:

When those tests were done in the BBC study - their projection for the double wythe masonry walls was in a perfect world - connections made only with metal brick ties - and no mortar in the cavity.

Which BBC study is this? I am not familiar with it. Cf my previous post for more information on the brick force. It may be metal ties between the wythes. I don't think the mortar in the cavity is significant because both wythes are on the same ground with no isolation. I may be wrong, and it won't be first time, or the last. :) Honestly, Andre

Andre, Sorry - I meant the IRC study you were referring to in your post..... Whether it acts as a single leaf or 2 seperate leafs is verydependant on whether the space between the walls was kept free of mortar droppings or not...... The fact that it ties to the same foundation or slab will limit it by flanking transmissions - but it will still act a a 2 leaf system if they are isolated otherwise from one another - and then the limiting factor becomes whatever is the weaker of the 2 links. Rod

Attatched pic is of brick force in use in my build, the link you supplied Andre was on the money. There is definately mortar mess in the cavity, how much i cannot say (thanks to builder incompetence), unfortuanately it is not a perfect world Rod. The brick force used was 9" brick force according to my memory. The inner wall is the only wall touching the slab but both the walls are on the same foundation.

Rod, i just want to confirm then, would you still stick with what you said and treat my cavity walls as a 1 leaf system, so i would put up drywall framing off the walls and fill the space half with wool and then close it up with drywall layers

rod gervais wrote:

AVare wrote:

I don't think the mortar in the cavity is significant because both wythes are on the same ground with no isolation. I may be wrong, and it won't be first time, or the last. :) Honestly, Andre

Whether it acts as a single leaf or 2 seperate leafs is verydependant on whether the space between the walls was kept free of mortar droppings or not...... The fact that it ties to the same foundation or slab will limit it by flanking transmissions - but it will still act a a 2 leaf system if they are isolated otherwise from one another - and then the limiting factor becomes whatever is the weaker of the 2 links.

Thanks Rod. As you have written in the past, the following is not meant in a disrespectful manner in any way, shape, or form. My statements were based upon the following logic. Droppings between wythes in a double block wall can be the weak link (there is a joke in there somewhere) in sound isolation for a wall and/or room. In this particular the case, the roof is corrugated metal with a light topping. In terms of the overall room isolation, the double brick walls even with droppings are not the limiting factor. I hope this helps explain my thinking. Please correct me if I am wrong. Andre

Hi Andre Just to clear things up, the roof is no longer a corrugated metal one, we ripped out the whole roof and replaced it with a heavy double roman clay/cement tile

Andre, understood - and I agree that one should be concerned with the weakest lnk - the only point a was trying to make was that the walls as they sit are going to act as a single leaf - regardless of the remainder of the construction. Eventually - should one find a way to repair/replace that weak link - they should understand what they are dealing with that remains. Sincerely, Rod

Ok guys, I have a few things i would like to confirm. My roof is a week link in my system at the moment, i know this and will sort it out. According to Rod my cavity walls are acting like a single leaf due to the fact that there has been mortar mess and the use of "brick force" to tie the two walls together was used. Must i now definately treat this as a single leaf? because of the fact that it is still a "semi" cavity wall will i still have more benefit from this even if it is to a small degree with isolation, than if it was a compact cemented double wall (true 1 leaf) . Below is a pic of my planning (sorry for the bad drawing, my sketchup was not at hand) i treated the cavity walls as if they were a single leaf. Notice also that it looks like a four leaf sytem now.

Straight words. The roof is your weakest link. The walls are not a concern.

thanks for your quick reply Andre :-) i edited my post

If i had to go as far and go with that room in a room design, how should it work out Andre and how does the idea for the roof seem? I'm not asking to be spoon fed information but what sort of solution should i consider for the tile roof?

I just got back from a construction site now where they are putting up slabs, it costs thousands to put up a slab for the roof, there are only two companies in south africa who make them and they then have to be transported and lifted with a crane into position which costs even more money. I also dont have access into my back yard for a crane.

I am not familiar with the construction materials that are common i south Africa so I reaching/guessing now. What you want is a double leaf with as much mass as reasonably possible. For the outer leaf, you already investigated a pre cast slab and it is not feasible. Can you (meaning structural safety wise) build a brick roof on top? Rod may have better ideas than I have. Andre

I had a word with the builder and got exact measurements regarding the cavity size ect. two sigle brick walls with a cavity of 50mm between the two. The single brick wall size is 220mm and the outside walls face is plastered an additional 15mm thick aswell as the inside walls face. The two single brick walls are connected with brick force at every 5 layers of brick. sorry to keep bringing this qeustion up but now with exact measurements, is it still acting as a single leaf and not MAM.

PreludetoJune. There are many companies making precast components pieces for Concrete slabs in South Africa. Certainly there are many in Cape Town and I suspect there should be a whole lot more where you are up North. I have a 6.5m Span floor and we managed to place the precast beams in place by hand (OK, several hands!), and then layed the blocks between the beams, all without any crane. Finally we used a concrete pump truck with extension boom to place concrete on top of precast beams. It is do-able, but does need engineering design to ensure compliance with building laws. You have a really massive outer leaf - great! I srongly recommend that you go with the timber-frame room within your brickwalls and independent ceiling framed on top of these walls, isolated from your brick walls or tile roof, with double layer of 12 mm Plasterboard and insulation. You could try your room as you have planned: If it really doesnt work and you want to, you could then consider the concrete slab on top of your brick walls to replace your tiled roof? You are right; it would cost about R 25 000 or $4000 to do it. Didnt we propose this solution in May when you removed your Tin roof? Good luck Marz

Hey Marz, how goes? long time no see on the forums! Thanks for the info, i think i am going to go with the rhinowall room in a room, with my rhinowall frames decoupled from my brick walls and a ceiling ontop of the rhinowall frames decoupled from the brick walls roof and ceiling, im sure this isolation will then be enough. Would you strictly suggest to use wooden frames or can i use the standard aluminium frames normally used in SA for the studs? Do you perhaps know if green glue is available in SA? Keep well man.

PreludetoJune Personally I have built Timber Frame houses in the past, so prefer this method instead of steel framing. Keep in mind the thicker you can make the walls the better as well. Some suggest 2 x 6's instead of standard 2 x 4s (IE 50 x 150mm or 50 x 100mm respectively) - so Timber frame is better to achieve these thicknesses. Typical steel framing is 3" or 75 mm I think. Standard in SA for Timber framing is 1.5 x 4.5's which machined are actually 32mm x 110mm - Better to get Planned all round - PAR - for uniformity of wall thickness. For added security, your wall sills on the concrete should be treated - Tanalith treated, to ensure no hassles later. I just used Tanalith treated throughout my walls. Be careful with the bottom sill and top wallplates - as you easily find a situation after 2 layers of ceiling where there is no place to fasten the wall plasterboards to. I use double sill and wall plates to ensure no problems - same applies to fastening the skirting boards, you may not have any sill left and then obliged to find the vertical studs. The recommended spacing of verticals is 24" IE 60 cm. Aim to have the ceiling beams sit on top of the vertical studs. Needs good planning! It is highly recommended to nail the Timber frames together and not be tempted to screw them together. I use galvanized Ring Shank nails for added grip. These come in 90mm and 120mm lengths. The 90mm are good for most joins, but sometimes you need the 120mm. I cant recall your room width, but you probably need around 2 x 6's for the ceiling beams - IE 32 x 144mm in South Africa. For longer spans, you may need to increase that to 220mm depth beams. For the Green Glue - I decided not to use it and did not research too hard, but have not seen any. I did order some stuff from the USA though - the Metacaulk Putty Pads from ebuildingproducts <[removed]> and that worked fine. So probably you could find a supplier to ship some if you cant find any. Dont stop now regards Marz