In Main’s cold climate, insulating existing attics to an R-value of at least .38 is recommended. It’s a dramatic step, and I’ve read a lot of research on the internet about it. I would chuck a 3/8" bit in a drill, mark 1.5" depth and drill blind holes roughly every 2' into the edges of 2x4s. Insulation can be installed either on the sloping roof, between and over rafters, or at ceiling level between or over joists. Cold Pitched Roof . Consider the location of the vapour barrier. Where I can see them less suitable are in eartquake prone areas since these roofs are very heavy (but still pretty common in CA). Powered by Discourse, best viewed with JavaScript enabled, Sistering roof rafters to increase space for insulation. Insulation Ideas & Inspiration. For instance, if the roof has 2-by-6 rafters and you want R-30 insulation, which is standard in many communities, you can add a 2-by-4, which will give you an 9-inch rafter space. The only good approach for ventilation would be to put in a ridge vent, unfortunately, we have a slate roof, which would make the ridge vent tricky and expensive. This means adding 75mm timber onto the existing 100mm rafters. I take it you want to extend the width of rafters so that more insulation can be put in. How is a 2x12 any more wood than a 2x8 plus a 2x3? Hang drywall by screwing into the flange you created (the 2x material … Reduces internal space and can compromise head height within the room. Repeat the procedure to add depth to all the rafters. Same wood, give or take an inch, and half the labor. As this requires fitting insulation above the rafters the roof covering will have to be removed in order to fit the insulation. Going from R39 to R40= 0.06% reduction in heat flow (not even near another 1% more savings for this last increase of R1!!! And please do NOT install those styrofoam baffles all the way up!!! How to extend a 2"x6" rafter armvz (Civil/Environmental) (OP) 18 Aug 03 08:58. For example, glass fiber batt or blanket insulation has an R-value of around 3.2 per inch, and the R-value of loose-fill cellulose is about 3.7 per inch. Using the open cell Icynene spray, you would get a lot less R-factor and would need the vapor barrier as well. Again, the thickness will vary depending on the material you choose to use. I’ll make it up to you next time now that I know. For the first part of the roof, it is behind the kneewall, so insulation isn’t as important. When handling wool, ensure you take enough rolls with you into your loft space. Trust the installers to get it right…after all, with the nailing flange on the insulation face, how difficult is it? As GBA senior editor Martin Holladay points out, Buckley is in Climate Zone 5, where code requires a minimum of R-38 ceiling insulation. An update on the situation for those who are interested. For the top part of the roof, it is above the ceiling joists (and the insulation), so also not as critical. The roof rafters are currently about 20" apart, made of 2X6’s (the house was built in 1915). Angle the nails sharply so all pass through the edge of the new board and into the existing rafter. Insert two additional nails, evenly spaced, between cleats, inserting them in the new board, 1/2 inch from the seam where the board meets the existing rafter. High-perfor-mance batts enable homes to meet these recommendations eas-ily and cost-effectively. Where does the water go? Insulation Installation. Insulating rafters with R-30, extending depth of 2x8 with 2x4 Finishing off a 3rd floor playroom and need to insulate the roofline, ceiling, and kneewalls. I assume the 2X12’s need to run the full length as one board, sistered to the rafter, to add structural integrity? Figure the rafter depth needed to provide the desired R-value. Then, use 3.5" deck screws in the holes to fasten the 2x4s to the rafters. However, it’s the middle section that’s key. Sad but true. The depth of rafter will obviously influence the thickness of insulation you can fit between them, but you can always extend the rafter by attaching a wooden extension to it, since the more insulation you can fit in place, the warmer the loft space will be. Measure the actual depth of your rafters and the width of the boards you purchase to ensure adequate rafter space. 12 inches --- R38. If the roof has no ceiling then the insulation can be placed between the rafters and ventilation maintained as described above - in which case the ridge should also have vent tiles installed to allow for through ventilation. As Larry has suggested would give you an R-factor of 19+ 2" of thermax insulation which is 14.4 would equal 33.4. Easy Fixes for Drafty Windows and Doors. If you plan on using fiberglass batts, make sure the ventilation baffles does allow the insulation to “breathe” into the moving air. I have renovated many vintage home and I suspect the reason for no soffit vent is due to timber framing which will not allow for any venting. • Make sure there is enough rafter depth to accommodate not only the thickness of the Celotex insulation, but also a If you want to extend the rafters farther, to cover a … If we didn’t use something to hold off the insulation, I’d be afraid the installers might push it right up against the roof. Icynene is great for the airtightness, but I’m wary of the upfront expense. The more I learn about American roofing systems, the more I am in favor for clay or concrete tiles that allow the roof to properly breathe. The roof rafters are currently about 20" apart, made of 2X6’s (the house was built in 1915). I didn’t say the low insulation level in the cathedral was the only reason, but one of the reasons. 6 inches --- R19. Water vapor will only condensate on these baffles and eventually soaking the insulation. To attach a cleat, place it flat along the side of the rafter, with the short end of the cleat touching the underside of the roof decking. Cut the top and bottom angles of the board to match the angles of the existing rafters. More Insulation Ideas & Inspiration in this topic. The thing that is nice about this method is the thermal break, the rafters don’t go all the way through. In this case, how much do you need? Q) Is it possible to increase the rafter depth but from the outside? The choice of where to insulate in your roof will depend on how this space is used we will explore the advantages as we continue through this guide. Dang dude didn’t mean to snub the “line jockeys”. 100mm concrete. One approach we’ve discussed is sistering each 2X6 with another 2X8, and then firring that out with a 2X3 to give enough depth to get R38 in there (you need 5.5" for the insulation, plus another 1-2" for air flow). Going from R1 to R2= 50% reduction in heat flow Where rafters are shallow (less than 75mm) a limited depth of insulation can be accommodated. So, the question then became, why worry about ventilation at all? Once the drywall is down remove all insulation between the studs. Another approach we’ve discussed is sistering the 2X8 “off” the roof, meaning the 2X8 is not overlapping the 2X6 for all 6", but maybe only for 4" or so. In this instance, you would need 9-inch cleats. (If you notice any condensation or dampness within the walls or on the insulation, allow wall to dry thoroughly before proceeding.) The GC seemed very hesitant about sistering the existing rafters with 2X10’s, let alone 2X12’s. Take that money and put it where it gives you a better return. This system can be made worse by adding gable end vents for the outer attic as they allow more air movement from the attic floor system and house below. Actually, none of the houses on my street have soffit vents, either (built in the early 1900’s when houses were drafty). When installing 2-by-4 lumber to existing 2-by-6 rafters, add the 2-by-4 width, which is 3 1/2 inches to the 2-by-6 width, which is 5 1/2 inches, for a total of 9 inches. Insulation and Fenestration Criteria Table 402.1.1 Insulation and Fenestration Requirements by Componenta CLIMATE ZONE FENESTRATION U-FACTORb SKYLIGHTb U-FACTOR GLAZED FENESTRATIONb,e SHGC CEILING R-VALUE WOOD FRAME WALL R-VALUE MASS WALL R-VALUEi FLOOR R-VALUE BASEMENTc WALL R-VALUE SLABd R-VALUE & DEPTH CRAWL SPACEc WALL R VALUE … Detail for the internal installation of woodfibre insulation to an existing roof; where existing rafters are not deep enough to allow 200-250mm insulation to be installed. Why not simply sister the rafters with 2x12s? It’s not actually necessary to increase ceiling joist depth for insulation because insulation does not require tall joist cavities. :shock: :mrgreen: You have given out too much Reputation in the last 24 hours, try again later. Do this on both sides of the rafter. More Insulation Installation in this topic. Both convection and conduction heat loss contribute to the problem. So again r-19 + 21 @3" = 40 Just add another inch and your at R-48 and what is nice is you do not need to add a vapor barrier. It creates a real thermal and air barrier, and you don’t have to worry about ventilation. There seemed to be a consensus opinion that gable vents are not worth anything at all. This polyurethan spray insulation closed cell would provide you with a 8 R-factor per inch. Increase rafter depth before insulating attic rafters. Depending on the specifics of the roof, it may be possible to fully fill the rafter depth or, in most cases leave a 25mm or 50mm air gap between the top face of the insulation and the sarking membrane. Alternate Insulation Method. They want to sell you a product/service and be on their way. You may want to consider applying a rigid polyisocyanurate insulation (typically R7 to 8 per inch) on the bottom of the rafters after installing baffles, continuous from eave to peak, and batt insulation between the rafters. Insulation reduces the upward flow of heat, keeping it inside your home longer. Twelve inches of the glass fiber batt insulation achieves R-38, and about 10 1/2 inches of cellulose will do the trick. Nathan, the contractors do not really care about your house after a few years. Only purpose is to hold insulation away from roof and maintain the needed air space. One of the worst items handled in an attic renovation/conversion is the air leakage at the attic kneewall down through to the ceiling below. One question that no one seems to know the answer to is what happens if the roof leaks? Positioning insulation between rafters where access is available may avoid having to increase the height of a roof by insulating above or, alternatively, reducing headroom or disturbing a historic ceiling internally by thermally upgrading below. I also thought about only sistering the portion that needs the insulation the most, which is the section that is not behind the kneewall, and below the ceiling joist. Space the cleats 2 feet apart on both sides of the rafter, but stagger the cleats from side to side, so you have one cleat every foot on alternating sides of the rafter. Remove all nails and screws from the now bare studs. And only use baffles where they are necessary, so the insulation can vent. In addition, if the basement is not already insulated, consider extending insulation a minimum of 610 mm (24 in.) Use cleats the same length as the width of the new rafter when added to the width of the old rafter. Which is one of the reasons there is so much ice damming on many of these older houses where the attic has been converted. Roof Insulation-increase rafter depth- Vapour-permeable membrane [Version ID #293] Author details Original Author: Admin Organisation: Overview; Revisions; Detail summary. There is a drainage system. In (native) Sweden, there are very few problems with these roofs, in rain, or in snow, and they last 50+ years. Attach a 2x2 or 2x3 along the bottom edge, face nailed through the OSB. It works well to increase the R value and furring strips and then drywall can be applied. I have pics that I would like some one to review, the rafters were 4 ft and know I exteneded them another 7 ft Thanks They have cardboard baffles as well, right? RE: How to extend a 2"x6" rafter SlideRuleEra (Structural) 18 Aug 03 13:19. Author details Original Author: Admin Organisation: Retrofit Pattern Book Overview; Revisions; Detail summary. While roof overhang depth can differ depending on the style of the home, standard overhangs extend outward about 24 inches. Use the baffles only to maintain the air space where the roof and wall meet, and no further. When you are done, these cleats will serve as side supports to hold the new 2-by rafter boards. Do NOT trust the paper on the insulation. Position the new board between the rafter cleats and insert two nails, evenly spaced, through the cleats and into the new rafter to hold it in place. So we extended our rafters with some two by fours, giving us the space to increase our ceiling insulation to R30. If the rafter is longer than the board, you will need multiple boards. They don’t ventilate, and are more likely to allow snow or driving rain into the house than air to escape (well, I exaggerate a bit). Another alternative would be to just spray the whole underside of the roof with SPF. Then you hang each from an existing rafter by overlapping the OSB on the rafter by ~2.5" and face nailing through the side of the top edge of your new makeshift rafter extender. Hi i extending my roof rafters and I used 2 1/2 inch bolts and 10 special rafter screws and I would like to see if some one can tell me if they are safe because I need to remove the main wall underneath the old rafters. How is this calculated? I’ve seen plenty of fiberglass insulation with all the R-value squished out of it, seems to be a common mistake. Adding Attic Insulation. But, it seems you also reduce the strength of the sister, or is it not really necessary anyway? Just NEVER remove a collar tie.. Yes I know that Brian. I’ve been talking with the GC about approaches to try and increase the depth of the roof rafters to get in more insulation, while at the same time allowing a baffle for air flow (I have a slate roof). I don’t know that they’ll be able to use the nailing flange on the batts, since the width isn’t going to be standard (the rafters aren’t 16" on center). Because the thermal resistance value — or R-value — increases with the thickness of the insulation, for the maximum energy-saving benefit you might have to increase rafter depth. Local building codes regulate the minimum amount of insulation contractors must install in new homes, but existing homes can benefit from roof insulation as well. Minimal raising of existing roofline. I’ve been talking with the GC about approaches to try and increase the depth of the roof rafters to get in more insulation, while at the same time allowing a baffle for air flow (I have a slate roof). For instance, if the roof has 2-by-6 rafters and you want R-30 insulation, which is standard in many communities, you can add a 2-by-4, which will give you an 9-inch rafter space. Glenda Taylor is a contractor and a full-time writer specializing in construction writing. The insulation can be placed under the concrete or between the concrete and screed. The thermax insulation would have to be foiled faced. It’s no sense getting to R40 if the payback for the last R10 is 40 years away., especially if it’s a more expensive than the earlier R’s. For details, see Figure 6-8 and Section 6.1, Insulating the basement from the outside. With that said your alternative are, gable vents or spray foam, the latter is probably the best choice. He’s already at the site and set up, so the extra R10 is pure insulation/labour cost. So, without sistering or firring out the rafters, I’m looking at only about 4.5 - 5" of depth, which is not much insulation whether you use batt or icynene. Both of these insulation types are commonly used to insulate attics. Remember that insulation is affected by the “Law of Diminishing Returns”. Nathan, Larry is giving you good advice and there are different alternatives and solutions, and this would be an alternative; Because warm air naturally rises, the attic or roof area of your home is your first priority for insulating. It’s measured per inch of material. Keep in mind that 2-by lumber is not 2 inches thick, nor is it as wide as its name implies. This is usually never properly airsealed and the outer attic is usually warm. Attach 1/2-inch wood cleats to both sides of the existing rafter. Since this product is closed cell, it will not allow water through and any leaks in the roof would take a long time to show up, so therefore, needs to be checked on a regular basis. How to Insulate an Old House. Measure and cut the insulation to the desired height (generally from the top of the footings to the exterior wall flashing). The idea against the 2X12’s would be that it wouldn’t be necessary the whole run of the rafter (since behind the kneewall insulation isn’t as critical). This will lower the ceiling height significantly. The disadvantage, however, is that insulation can not always be inserted to the required thickness because of insufficient rafter depth, though this can sometimes be overcome … Figure the rafter depth needed to provide the desired R-value. As Larry has suggested would give you an R-factor of 19+ 2" of thermax insulation which is 14.4 would equal 33.4. Moderator Doug Aleshire had a great image in another thread, hope he won't mind me referencing it. It would be a lot of wood, too, I imagine. It reduces the ceiling height some but the added insulation value is worth it, IMO. He felt it would be too unweildly. However, has anyone seen any practical experience where this approach has led to problems? So, without sistering or firring out the rafters, I’m looking at only about 4.5 - 5" of depth, which is not much insulation whether you use batt or icynene. The standard residential roof, framed with 2-by-6 rafters, is an optimal spot for adding insulation because heat escapes through the roof, resulting in higher energy costs. This extra R value may pay for itself in as little as 5-6-7 years (depending on fuel types/costs) but as fuel prices go up in the future, the payback time decreases. The house has no soffit vents. The insulation has no horizontal seams that break the drainage path. Roof Insulation for Increased depth Rafters. She also enjoys writing business and finance, food and drink and pet-related articles. That seems like a potential option. Ventilation IS necessary, albeit maybe less so if you have a slate roof that “breathes” towards the outside (compared to torch down and other “sealed types”). Will a 4' overlap an two 1/2" bolts suffice? I’m currently renovating an unfinished attic or a front-gabled house. R-value is the measure of an insulation material’s ability to resist heat flow. of polyiso foam,” Holladay writes. insulation levels of R-19 for side-walls in most areas. So you end up with an L, 8" on the long side and the width of the lumber on the short. That means you’ll stay warmer, and your heating system will not come on as often—reducing your utility costs! I would like to know how to extend a 2"x6" southern pine wood rafter so that it keeps the same structural properties as if it was a continous member. But, it’s a good question. It both allows for added space as well as stronger frame members. Insulation, high efficiency windows and doors, heating and cooling equipment and caulking are just some of the purchases that qualify. By installing high-density 8-inch fiberglass batt insulation, the rafters will then meet an R-30 roof insulation standard. Thermal bridging through the rafters . Insulation can be placed between the ceiling joists. To achieve the building regs U value of 0.18 I need 125mm celotex + a 50mm air gap. If you can get the R’s in cheaply using lower cost insulation like blown fiberglass or cellulose in an open attic blow, with today’s fuel prices, R45-50 may make sense! In order to increase the “depths”, furr out existing 2x6" with a 2x2" or a 2x4" screwed and glued in place. Traditionally, to achieve an R-value of 19 in sidewalls, builders install standard insulation batts along with insulated sheathing. Needless to sya, do not skip on the vapor barrier. You must address both to have a well performing assembly. Stay away from “Durovent” or other type of manufactured baffles out of styrfoam. Custom made baffles out of “peg board” or some type of “mesh”/netting would be better. 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