Eaves
What are eaves?
The eaves within a roof assembly refers to the rafter tails as they project past wall plates and form the overhang of the roof structure. In a practical sense, the overhang of the eaves protects the intersection where the external wall meets the roof from driving rain and wind. Aesthetically, the eaves can provide a more balanced aesthetic to a building and give a decorative appearance. Additionally, the eaves assembly provides suitable ventilation to the main structure of the roof, as well as an appropriate location for the installation of the gutter.
How are the different styles of eaves created?
Exposed eaves
Exposed eaves are the simplest form of eaves, requiring the least amount of work to assemble, also providing a more traditional aesthetic. This style sees the rafter tails projecting past the building, with no covering underneath them. As such, the tails are on display - sometimes shaped in a decorative fashion. Planed wide boards, the same thickness as the roof battens, often tongue and groove, are installed on top of the rafter tails beyond the wall plate to provide a clean finish to the underside of the eaves, hiding the roof tiles/roof covering from below. A finished timber fascia board may be installed on the rafter tails - at the very least a small, finished timber is installed to provide a fixing for the lower roof covering components such as the eaves guard and gutters. As the tails are on display, it's important for them to be cut neatly and uniformly to display a professional finish. Where rafters land off of the on-centre layout within the roof, these irregularly spaced tails may be removed beyond the plate, with false tails being installed on centre to maintain a consecutive appearance from the outside of the building. These timber open eaves are often painted or stained to provide weather resistance as well as an aesthetic finish. Solid blocking is commonly installed between the rafters on top of the wall plate to physically block wind, animals, and insects from entering the roof space via the holes that would otherwise be present.
Closed eaves
Closed eaves are a form of eaves that are formed through the use of fascia and soffit boards to cover the rafter tails. This aesthetic is more modern, providing a clean and more finished look, though requires more labour and materials to produce. A plumb and seat cut are made on the rafter tails in order to receive a fascia and soffit respectively.
What is a soffit and fascia line?
Beyond the wall plates and the birdsmouth notches that are cut into the rafters, a portion of the timber typically projects past the exterior masonry. This section of the rafter is known as the “rafter tail” and serves to support the soffit and fascia assembly, as well as the roof covering that overhangs the building. The fascia is a construction component that is installed plumb on the end of the rafters to create an aesthetic stop to the end of the roof. It also supports the installation of the gutter and provides a kick to the last row of roof tiles that are installed on top of the rafters. Traditional fascia board is machined from timber and is planned to a nice finish. This timber is then painted or stained to protect it from the elements. A groove or “dado” may be routed in the back of the timber to receive a thin plywood soffit. This soffit is installed level onto the bottom of the rafter tails. It may sit up against the external skin, or possibly on top of the top course of the external masonry. This method of an all-timber construction is relatively dated, and whilst still occasionally used, modern plastic materials have taken the forefront of this assembly.
A timber backer board is still installed plumb onto the ends of the rafters in order to receive the plastic fascia capping. Plastic flat soffit or plastic hollow tongue and groove soffit is used in lieu of traditional timber soffit. A timber ladder may be assembled and installed between the rafter tails in order to support the soffit as it meets the masonry. Here we shall look at how the rafter tails are prepared to receive a soffit and fascia assembly.
What are the criteria of a soffit and fascia line?
The soffit and fascia assembly are a critical component within a roof assembly to attempt to perfect. Of all the carpentry components that we install, across all the different stages of the construction, this is one that is imperative to get right. Especially on low roofs such as bungalows, when anyone walks down the driveway, they are looking directly down the line of the fascia. If there's a small deviation in the roof structure, no one is going to be able to see it from the ground - especially if it features ridged tiles. The fascia line on the other hand - especially when capped with a shiny uPVC fascia board - is going to show every single imperfection in the run. In every aspect of carpentry, we should try and achieve perfection, and most of the components that we create are on display to some extent. That being said, the shear length of the fascia - as long as 15+m for common residential properties - adds a degree of difficulty to the process. As such, we must take extra care to ensure that these lines are perfectly straight from end to end without any deviations along its length. The same is true for the installation of the soffit, as we’ll be able to see any humps and low spots against the level brick courses of the external skin.
How are soffit and fascia lines created?
The deciding factor in the location of the soffit and fascia line is the width of the soffit off of the external masonry. Typically speaking, the width of the soffit off of the masonry is determined in a broad sense by the pitch of the roof. The rafter tails of a shallow pitch roof project past the masonry further for longer at a suitable level as opposed to a steeper pitch. This is commonly seen in low pitch bungalows that feature relatively wide overhangs. Either way, both the soffit and the fascia must be supported by some portion of the rafter tail, and so suitable cutoffs must be made to accommodate this. The setting out of these cuts can be done on the pattern by a process of stepping out, though it's easier to achieve and visualise once the roof is pitched. By pitching a pair of rafters based on the pattern, we can establish the soffit and fascia cuts before bringing them back down to the cutting station to make these cuts on all of the other rafters before they are installed on the roof. Alternatively, the soffit and fascia line can be cut after the fact if the rafter tails are left long. Either method is appropriate, with the deciding factor being time and space available.
For the sake of example, we will look at a rafter that is already pitched in place. A plumb line can be struck up the side of the rafter in line with the external skin of masonry. If the soffit is going to sit on the top course of masonry, then a level line should be struck across from this point too. If not, we can determine the height of the soffit installation at a later point. Flat soffit comes in widths that increase in increments of 25mm, starting from around 100mm. A common width would be somewhere around 150mm-200mm. Hollow soffit can be cut to any length, but we still aim for these standard sizes. By measuring off of the plumb masonry line at an appropriate width (200mm) in this instance, we are left with the location of the front edge of the timber backer board. The very edge of the soffit is nailed to this backer board, with the fascia capping covering the nails/screws, and being fixed to the timber backer. This timber backer is typically a 1” wide timber. By measuring back from our line 1”, we now have a plumb cut line that is suitable to receive the timber backer at a distance away from the masonry to leave us with a soffit width that we’re happy with.
We now need to determine the width of the timber backer in order to find the height of the soffit cut. Depending on the roof covering system, a specific amount of upstand above the rafter is required for the timber backer. Slate roofs require little to no kick up at their termination point. A tile vent is installed on top of the backer -this is typically 1” tall. Therefore, we can keep our timber backer board 1” above the rafters to allow for the vent to go on and kick the tiles up to an appropriate amount for the doubled battened slate system. For clay tiles, the upstand may be as much as 2” plus the vent to allow for the appropriate amount of kick up. With that upstand in mind, we often aim for a fascia width of around 150mm. We can therefore find the location of the seat cut to receive the soffit with our upstand in mind.
With the rafter tail marked out, we can cut to our lines and use this rafter as a pattern to cut the other rafters. Alternatively, if the rafters are all already installed with the tails long, we can find these marks at each end of the run and pull a string line between the two points to create a straight line all the way across the tails. We can use a small level to create a plumb line off of the line on each of these tails. We can then cut to these lines to create the plumb cut on all the rafter tails. Using a circular saw really helps here to keep the cuts straight, as the saw naturally wants to fall straight down, and the flat bottom of the saw references perfectly square on the side of the rafters. It can sometimes be tight to get a circular saw in there though, so a handsaw must be used. From here, we could install the backer and cut the bottom projection off afterwards. We could also cut them off before the backer goes on, slightly short of the bottom of the backer, so that they don't project past it. This is acceptable, as the soffit will be pinned to the backer, and not the rafter tails. Screw the backer on temporarily with the correct upstand above the rafters - a block can be used here to maintain consistency.
With the backer screwed on at regular intervals, we can cast our eye down it to check for straightness in both directions. A trained eye will be able to easily spot deviations in the straightness of the timbers. As we round side the timbers, it's likely that the middle of the boards will have to be pushed down slightly to straighten them. If any bulges are present in the run, the screw can be removed, and a saw can be run down the back of the backer to remove some material from the rafter tail and push it back. If the board dives in at any point, a packer can be placed behind the backer to push it out again. If uncertain, a string line can be pulled between the two ends across the face of the backer, and the three-block trick can be used to straighten the timber. Overall, we’re looking for a tolerance of no more than a few millimetres.
With the backer installed, we can now move on to installing the soffit ladder if one is required. If the soffit sits on the masonry, it can be installed at this point and simply pegged down onto the masonry with battens nailed to the side of the rafters. To create a soffit ladder, lay battens across the rafters and mark the locations of the rafters. Calculate the length of the studs that will form the soffit ladder by measuring down from the side of the rafters to the intended height of the soffit. With the studs cut, simply screw them to the batten next to where the rafter marks are located. Once assembled, the ladder can be flipped upside down and placed at the soffit line, with all of the studs sliding neatly up next to a rafter. Screws can be used here to fix the ladder in place. Each stud can be adjusted to the correct height by using a small level to level the soffit ladder off of the perfectly level and straight timber fascia backer. With the ladder installed, the soffit can be pinned on.
Once the soffit is in place, the plastic fascia capping can be installed over the face of the timber backer, with the lip of the fascia covering the fixings in the front of the soffit board. Equal spacings of the Polytop fixings should be used here to create an aesthetic look. Once all of the fascia is installed, the plastic joiners and corners can be installed, and the guttering is ready to be installed.