Browse Forums General Discussion 1 Apr 20, 2020 3:15 am Hi, I am building a new home in Brisbane. I am hoping I might reach some of the energy efficiency conscious folks who understand roof truss designs. My builder (for a new home) is about to ask for the roof truss designs to be done. I am intending on having a 60mm anticon with r2.5 ceiling batts. I did some trigonometry calculations and I have detected an issue with the lack of space in the roof to install the insulation, in particular near the eaves. See image attached (sketched in red pen) I want to ensure the following requiremens are met: 1. Eve's are flush with window header (which means it needs to be "type A construction" as shown in attachment in black pen) , and 2. There is enough space between top chord and bottom chord to allow for the anticon blanket and bulk insulation to be installed (min 180mm space). The other attachment shows this is a problem.... Does anyone know what can be done to solve the problem? I have researched a bit and apparently there is such a design called "Raised Heel" Truss which allows for more insulation space, which would help address requirement 2 but may compromise requirement 1. Both requirements are important. Can anyone suggest anything? [img:81jvchgd]https://forum.homeone.com.au/u/76977_1587312841.jpeg[/img:81jvchgd] [img:81jvchgd]https://forum.homeone.com.au/u/76977_1587312846.jpg[/img:81jvchgd] [img:2nbx7azb]https://forum.homeone.com.au/u/76977_1587313151.jpg[/img:2nbx7azb] [img:2nbx7azb]https://forum.homeone.com.au/u/76977_1587313153.jpeg[/img:2nbx7azb] Re: Truss design - enough space for roof insulation 2Apr 22, 2020 12:56 pm If you are going with eaves, make sure you specify 'Cantilevered Eaves' as this will mean the overhang doesn't angle down towards the ground....the bottom chords extending out for the eaves are parallel with the ground. --------------------------------------------------------------------- Check our Homeone build blog here Re: Truss design - enough space for roof insulation 3Apr 22, 2020 10:42 pm Darb, yes, as per my intro, I am building to "Type A" construction, which is diagrammed and will show you the type of eve I have chosen. My intent of my post was to focus on this point: I want to ensure the following requirements are met: 2. There is enough space between top chord and bottom chord to allow for the anticon blanket (60mm) and bulk insulation to be installed (min 180mm space). The other attachment shows this is a problem.... Re: Truss design - enough space for roof insulation 4Apr 23, 2020 10:06 am Problem is none of your images or links worked, so just upload the images direct to homeone if you would like. If you are going with cantilevered eaves then I don't see an issue. I had 600mm eaves and over the external wall top plates I installed R4 ceiling batts (195mm) plus over the top of that an R2 roll (90mm) and had plenty of space to the top chord for more. [EDIT]....I forgot I actually had 2 x R2 roll over the top plates.....so add another 90mm! LOL and you are only asking for how much? You are worrying over nothing. I think you need to research more about anticon blankets and how they are installed because they don't go in between the top and bottom chords, they are installed over the roof battens, directly under the metal sheets or tiles. Anyhow like I said cantilevered eaves is what you need, but it's then up to you if you want to pay attention to someone who has already built last year and coordinated all the insulation and air sealing work myself. Good luck with your build! Also why the heck would you only go R2.5 for your ceiling batts? I understand warmer climate....and yes anticon blanket but the additional cost to upgrade to say R4 is minimal. I think you should rethink the R value of your ceiling. Oh and while I am feeling generous, make sure you do what I did and properly seal up all your top plates<>plaster joins in the roof before the insulation goes in. Especially over any CSDs, these are terribly sources of air leaks and insect penetrations. I could go on for pages on all this stuff, as our builder gave us permission to do most of this work ourselves....luckily too as their trades typically don't give a crap about this type of thing. --------------------------------------------------------------------- Check our Homeone build blog here Re: Truss design - enough space for roof insulation 5Apr 24, 2020 8:15 pm darb74, just omit the prefix and suffixes of those web links click on these instead u/76977_1587312841.jpeg u/76977_1587312846.jpg u/76977_1587313151.jpg u/76977_1587313153.jpeg Stewie Re: Truss design - enough space for roof insulation 6Apr 26, 2020 3:00 pm IMHO the solution is relatively simple, in this areas where angle is not allowing you to install batts, you fit insulation blanket in between and (where possible) under rafters and cover/fill installation with OSB boards from both sides. Re: Truss design - enough space for roof insulation 7Apr 26, 2020 4:40 pm In the drawing in red pen there doesn't seem to be the structural elements of the roof that give you the space for the insulation. Once you allow for the roof battens and rafter there is room for the ceiling batts. Unless I'm missing something from your drawing or explanation. Accessible Carpentry & Cabinets accessiblecarpentry@gmail.com accessiblecarpentry.com.au https://www.facebook.com/pages/Accessible-Carpentry-Cabinets/583314911709039 Re: Truss design - enough space for roof insulation 8Apr 27, 2020 10:37 am Yeah the drawings in red marker don't make sense to at all. You don't even have the 90mm truss chord width indicated, and no eaves at all? Even without eaves there is a slight truss overhang to allow for fascia and gutter attachment etc. It is fairly simple really, if you have eaves (especially 'cantilevered' type) you will have plenty of space for bulk insulation. Like I said previously we placed R4+R2+R2 over our top plate area so around ~360mm and still had space for air flow through the brick wall cavity --> roof. With no eaves (one east section) I could only add the R4 and one R2 roll was pretty much touching the sarking, so had to trim it down. Eaves are great for so many reasons, including insulation --------------------------------------------------------------------- Check our Homeone build blog here Re: Truss design - enough space for roof insulation 9May 09, 2020 5:09 pm darb74 You don't even have the 90mm truss chord width indicated Big assumption here. pending span, material grade and manufacturer, it could be 63mm chords (which obviously makes it worse) Regardless, what about a dropped bulkhead along the section where there isn't enough height for the insulation to be installed?? Re: Truss design - enough space for roof insulation 10May 09, 2020 8:32 pm I'm absolutely no expert, but reading a post on the My Efficient Electric Home (MEEH) Facebook group, I read that for most roofs you're not supposed to insulate over these eaves. This is because most roof space are supposed to be ventilated, to remove condensation & so mould growth. Insulating over the eaves blocks this area for ventilation. In this case you're only supposed to insulate above the internal ceiling. Hopefully others with more knowledge will chime in on this. I agree that R2.5 is inadequate for ceiling insulation. Your Home recommends R4 for Brisbane. You should put R2.5 in the walls though. Re: Truss design - enough space for roof insulation 11May 10, 2020 12:41 pm ddarroch I'm absolutely no expert, but reading a post on the My Efficient Electric Home (MEEH) Facebook group, I read that for most roofs you're not supposed to insulate over these eaves. This is because most roof space are supposed to be ventilated, to remove condensation & so mould growth. Insulating over the eaves blocks this area for ventilation. In this case you're only supposed to insulate above the internal ceiling. Hopefully others with more knowledge will chime in on this. I agree that R2.5 is inadequate for ceiling insulation. Your Home recommends R4 for Brisbane. You should put R2.5 in the walls though. Anticon 60 has an R-Value of 1.3, so 1.3 + 2.5 = 3.8. Depending on color of roof, min requirement is either 4.1, 4.6 or 5.1 but the above is only insulation values, no total system. A further issue is that with the suggestion of option B you will need a cantilevered truss, which will be more expensive It's hard to comment as the photos area bit dark ( you might need a new 15 - just got one and wow ) Jokes aside, I can see one member that is cracked. I would find a… 2 2195 dimensions on your original plan are inconsistent and with accurate dimensions (including site plan, upstairs and down) i could make a proper scale drawing with furniture… 3 7484 |