A few weeks ago a couple who are building in the western United States contacted us through our blog and asked us more specific questions about building with AAC. We are very excited that others are considering using this material and love the questions they posed to us. We thought it would be helpful to others who might be considering building with AAC if we posted the questions and answers (or just our experiences so far) on our blog.
Fri, 25 May 2007
Q: We are trying to figure out which size blocks to use (8, 10, or 12). We’re in the mountains of Boulder at 7500 ft, and were told 8 inch should be sufficient, but we have concerns still about whether that’s enough R value. What did you use?
A: We are using an 8″ block and also u-blocks and o-blocks. Really the 8″ block just made the most sense to us. Our site is not huge so we wanted to conserve space, the 8″ does have a good r-value for our area, and the 8″ seemed to me the easiest to handle. The thicker walls would be nice aesthetically but were not really needed for us. We have been told that for our area the 8″ block has an R-value equivalent of 16 but also to consider is the much tighter construction with AAC so the value may actually be higher. In a separate email I am forwarding you some information we received regarding the R-values that I think you will find helpful.
The AAC-4 is a stronger block than the AAC-2 but I am not sure of the exact numbers. The data is on the AAC websites if a structural engineer needs them.
We looked at (and went to) Ringgold, GA to see the Safecrete operation some time ago. While they sold us on AAC, their factory seemed not to be in production. [**UPDATE: We have been contacted by Safecrete, telling us that they are producing blocks. See post below**]. We also looked at Contec in TX, but their block ships from Mexico, so the cost of shipping was too prohibitive. We went with Aercon, but you may find Contec to be cheaper shipping-wise for your location. With Aercon, we got AAC 4 instead of AAC 2 with Contec, so this may be a consideration.
Q: With manufacturers, it appears that Texas Contec also buys from Mexico, so that’s where it would ship from? So I guess we need to price out Florida vs Mexico in terms of block and shipping costs. I think there might be a difference in fly ash content, too (with Mexico not having any…which we actually prefer.)
A: From our research we heard about fly ash being used in the block that is made by Safecrete in Georgia. Our blocks from Aercon did not have fly ash.
Q: We also haven’t yet figured out approximately how many blocks we’d need. I’m curious how many you needed and the total sf of your perimeter?
A: Amount of block- this is still in question to date- probably by the end of next week I can give you an exact number. I discussed our designs with Contec through the design process to make sure our design would work with AAC. The material seems versatile enough that it pretty much works with any design. When our design was finalized we paid them to create shop drawings and a block count. It’s still questionable whether that was money well spent or not? It was helpful and continued our ongoing discussion preparing for construction- so for now I’m going to call it money well spent since this is a new material for us. Charles Smith at Contec was very helpful to our project. Our contact person with Aercon is Don Perkins. I can get phone numbers and emails if you need them.
With our contractor we kept analyzing how much block we needed. I think we are finding that Contec’s number was pretty close and we were calculating too much. Our house is 3273 sq ft. Two story, 10′ high ceilings down, 9 up. We ordered 53 pallets of block with 60 blocks in a pallet with a portion of this being u-blocks for lintels and 2 courses at the 2nd floor level and o-blocks for the rebar cores. The block came in three flat bed trucks. As of today’s on site conversation it looks like we have plenty of regular block but are running low on u-block and will place the second part of our order next week. We intentionally knew that we would order a bit more block once construction started. It just made sense to us to order three trucks full of block, get started, and then request more.
We also ordered the repair mortar and the special AAC mortar. I am not sure the repair mortar has been used. The AAC mortar is a must. The block company will also help you estimate how much you will need.
My husband ordered a package of special AAC tools from Demand products. They all arrived undamaged. The damaged package on our blog came from Taylor Trading Company. The masons have been bringing their own gas powered circular saw press to the site to cut the block as well as using a hand saw.
Q: And did you do any interior in block?
A: We are using wood frame 2×4 construction for the interior walls and 14″ deep wood joists for the joists between the 1st and 2nd floor. We are also using wood trusses created with a slope for the roof. We thought about using AAC for the roof but somewhere in the construction drawings I came to the truss conclusion, primarily because they can be designed to slope which is needed for our low sloped parapet roof.
Q: Do you have a good ballpark for labor costs to install? Did you use people already trained in AAC or did you have someone train you? Are you going to use their special stucco on the exterior and regular plaster interior?
A: Our ballpark number for labor costs are $25,000. Our labor costs are probably fairly low in Memphis? I can give you more exact numbers pretty soon if this helps? You labor costs may be very different?
The masons have been great with the material. There was a bit of trial and error in the first hour when they started and then things went smoothly. We had a sales rep named Don Perkins who is familiar with the material on site the first morning for some helpful tips. No special training at all for us or the masons. The primary mason was familiar with unique masonry systems such as the Isokern fireplaces so things just clicked when he learned about AAC. I thought there would be a much greater learning curve.
Sat, 26 May 2007
Q: I’m also curious what your average temp is in the winter?
A: Our winters are very mild. Mostly in the 30′s in December and January. We might get one snow and that is just a few flakes. Memphis is hot and humid.
After I sent you the email last night, Dave said that the AAC-4 we are using has an r-value or e-equivalent of 24. The numbers I sent you are for AAC-2.
Q: Are you finishing interior walls with a certain plaster/other?
A: We plan to use the AAC based stucco for the first coat on the exterior (because it has a different moisture content than typical stucco) and then the two final coats of just normal cement based stucco. No metal lath, just applied directly to the block. We plan to attach drywall directly to the interior block walls with the special drywall nails for AAC that can be ordered through Demand products. The plaster interior would be nice, but we will probably use drywall.
Q: For people who are chemically sensitive can you tell if the mortar has strong fumes/smell after it’s been applied and dried?
A: The chemical sensitivity is hard for me to say? I am not very chemically sensitive so I would be afraid to judge this. In my opinion I have not smelled any chemical odors in the block or the mortar. There is a dust when they cut them but no smell that I have sensed. Again I might not be the best judge. I’ll try to consider this when I visit the site and I’ll let you know.
Don Perkins was very helpful to us and we received our block quickly without delays. Charles Smith was easy for us to call also. I can find cell numbers for you next week.
Q: Just curious if you had any window installment issues? We’re thinking of triple pane fiberglass, maybe from Fibertec (for energy efficiency). What did you end up going with?
A: I can try to enlarge some plan images to send to you soon and I’ll elaborate more on our windows and include a window detail. We are using wood clad with metal casement windows by Kolbe & Kolbe.
Tue, 29 May 2007
Q: I’m wondering if you think it’s critical to use an engineer who has AAC experience or not? We have someone who has worked with straw bale, but should we look around more? What were the key issues you feel like the engineer faced?
A: The engineering was a point where we had to pause and analyze. Our house got double engineered which opened up a few questions, not problems, but a discussion.
I work closely with a structural engineer at work so I asked him to review our drawings. He was familiar with straw bale and AAC. I think he had done two AAC structures in Nashville before. This was helpful because he knew the material. But really any good structural engineer who is familiar with residential construction and masonry construction will not find the AAC a problem. There are engineering codes for AAC. We knew that we needed the house engineered for the size of the anchor bolts (they attach the floor trusses to the AAC wall), foundation details, etc. and the AAC walls became part of the engineering package. I really needed the input of the structural engineer early on to ask questions and reassure me I was on the right track. It was part of my process with the design.
Later when we were nearing time to order our block, I sent the drawings to Contec for shop drawings and to have their engineer review them. In my opinion they were actually over engineered; more reinforcing than what our engineer had recommended. I am sure what they recommended is wonderful and will create a super sturdy house, but it was just a bit more than what we, our contractor, and our local engineer saw as necessary. I spent several sleepless nights during the reinforcing debate. Our house is very solid and is definitely reinforced, but in the end we found a happy medium on where to reinforce and what to leave out without causing any structural issues. I’m making a long story short on this. We have vertical reinforcing at all the corners, specific places along the wall and at all sides of window and door openings. We are using reinforced u-blocks with rebar and concrete at all lintels and two courses of u-block bond beams at the second floor connection and at the roof. Both our engineer and Contec’s sized the rebar and most of it came in the same. Since this was my first time dealing with AAC and because I did not know how detailed the shop drawings would be I felt that it was necessary to have our own engineer from the start of the project. If you are on a slope this will probably also make sense for you.
Also Contec’s engineer is in Mexico and ours is here in Tennessee so it made calling to ask questions much easier to have our own engineer. I am not sure about the engineering process with Aercon which is who we eventually ordered our block from.
Advice: Also we received a cd of pdf files with details and a notebook of information form Contec. This was extremely helpful! After researching, they had the most information that was the easiest to access. Most of their information can also be downloaded from their website. Aercon’s website does not have as much information. My first choice was Contec to order our block from because of the ease in getting and receiving information from them. The only reason we ended up using Aercon was that their shipping costs were slightly lower. I told their sales rep to update their website to make it more user friendly.
Thu, 07 Jun 2007
Q: Did you use ICFs for your foundation? We’re debating pouring cement for the walk out basement, or using ICFs perhaps.
A: We actually considered ICF for the whole house and researched this option. We decided on AAC because it just made more sense to us and seemed easier to work with. I have heard that ICF is great for basements (check the livemodern website there are several ICF houses being blogged). I think that AAC can be used for foundations and basements but it must be well protected from water. Our foundation is several courses of CMU then a slab on top of that – very basic. This is the typical method for this area since we have such mild winters, flat land, and excavation is very expensive for us. All of the older homes have basements and we are sad to loose this feature.
Look at our blog and think you will see the transition from CMU to AAC. We will have an expansion joint at this area that you will see in the stucco just to help prevent cracking between the two materials.
Our project was on hold the last week due to ordering some materials and a sub locating a window opening incorrectly- not happy with that! and it got moved today. We should have more blog posts soon as construction has resumed.
Thu, 07 Jun 2007
Q: I guess you’re using the AAC stucco – curious if subs find it the same to work with as regular stucco when you get to that point. Apparently there is a stucco from CA that doesn’t crack and acts as it’s own drainage plane. Not sure we’re “allowed” to use anything other than what AAC recommends though!
A: Our understanding with the stucco is that you need the AAC specific stucco for the first course because it has a different consistency than regular stucco. The following layers (typically stucco is three layers so the following two) would be whatever type stucco you want to use. Again our understanding, check with the manufacturer and the stucco installer.
Q: We’ve run into a problem with how to support the main floor bump outs now that if they are made out of AAC.
Do we need to extend the basement walls to support the upstairs bump outs, or is there another way? Do you know if it’s possible to do the bump outs in wood frame? (We’re still waiting for an engineer to have time to look at the plans).
A: I’m not sure about those “bump outs”? I would call them cantilevered bay windows. The easy solution to me seems to carry the pump out to the floor below to support it. With the help of a structural engineer they may have a solution for creating the cantilever structure and the AAC is really a skin. I kept feeling conflicted about mixing wood with AAC but it is not strange at all.
The block can be cut to form most shapes. The architect should be thinking of the material as CMU that is easier to work with. The AAC people may also be able to help you and the architect figure out the design.