So many individuals question driveway repair and construction that it appeared logical to offer a brief summary and education page on the construction of the proper driveway. These parameters and comments pertain to both the residential market as well as any industrial or commercial driveway installation.
As with any proper foundation, the ability of a driveway to sustain repeated traffic, as well as different types of weather conditions, is based upon the preparation of the sub base of the driveway. What is the sub base of the driveway? This is the material that the actual driveway rests upon, below the first course of asphalt.
Summarized below are some aspects of proper driveway construction that should be understood to enable the proper installation of a driveway that will have both, longevity and characteristics that will compliment your home or commercial structure for several years to come.
- No installation of a driveway surface, whether it is asphalt, concrete, stone or even a porous gravel material will withstand the effects of weather and use unless the sub base of the installation is adequate. The sub base of the driveway is the KEY to success.
- The layout of the driveway should consider the following parameters;
- Drainage / the proper drainage of any driveway surface is important to its ability to withstand heavy weather conditions. The drainage should always be away from the structure and off to the side of the driveway. This can be accomplished by either a crown in the driveway, which is basically a higher center, sloping down to each side of the drive, or by angling the drive directly off to one side or the other of the entire driveway. The discharge of water off the driveway is important to regulate the puddling as well as the erosion tendency of channeling water. The driveway should be graded to allow what is referenced as sheet flow over the driveway and not a concentrated linear flow, which can cause excessive erosion.
- Structure entry / the driveway should be laid out to access the entry to the garage or whatever point of entry is required for the structure, with a slight grade away from the structure. The drive should always be positioned to allow the positive flow of water away from the entry point of the building.
- The curb cut of the driveway, where the driveway exits to the street, should be positioned to maximize sight distance for maximum safety. The drive should never exit at the crest of a hill or on a curve. Any minimizing of site distance will plague the occupants of the structure as long as they use the driveway and will cause a substantial safety hazard.
- Unless the driveway is considered to be an aesthetic entity of the entire property, the driveway should be the shortest distance between the entry point of the structure and the adjacent street. Long and serpentine driveways will add to the cost of the drive as well as cause maintenance issues in the future care of the entire property.
- The driveway should be boxed out at the very beginning of the project. To box out a driveway is the operation of removal of all the topsoil and non-supportive material that exists within the area of the intended driveway. All of the material that will not be a part of the actual sub base of the driveway should be removed during the clearing and grubbing of the entire project site. If this is properly performed immediately upon access to the site, all construction vehicles, concrete trucks, structural steel loads, etc. will enter the construction site on this boxed out portion of the site, intended for the driveway. In this manner, for as long the construction may require, the driveway is being compacted on a daily basis by the construction vehicles and deliveries to the project site. Repeated compaction on a daily basis is the best method or establishing the proper overall compaction of the driveway area.
- Once the majority of the construction has been completed on the project and the heavy deliveries have been completed, the driveway should be constructed. The important aspect of any driveway installation is the sub base preparation. The area that will incorporate the driveway should be excavated to the point of substantial virgin ground, if possible. This is the point where there is no topsoil and only the original earth remains under the driveway sub base. All rocks and miscellaneous obstructions must be removed from the area of the driveway. If there is ledge present, then the ledge must be cut back to allow a substantial cushion layer of porous material to be compacted on the top of the ledge.
- A porous granular material, should be installed in the area that the driveway is to be located. This porous granular material should be nonorganic and properly graded to allow percolation of water and the ability to properly compact. The ability of a material to compact is based upon the gradation of the material. The gradation of the material is the percent of fines, medium size particles and larger particles that will allow the proper compaction of the material. All material has, what is called a packing factor. This packing factor is the ability of the material to organize itself into the most compact matrix of particle sizes. Once this material is compacted, the structural ability of this material to withstand loading is increased. The better the material arranges itself into a compact mix, the stronger the sub base will be. It is recommended that a minimum depth of 12 inches of controlled material be compacted under the intended driveway surface.
- It is my opinion that the profiles of the entire driveway should include a stabilization fabric over the top of the initial sub base material. Whether the driveway is in an area of compromised material, meaning the compaction is not as high as preferred, or the driveway is totally stabilized and properly compacted, I feel that based upon the minimum pricing of the stabilization fabric, it should be installed.
- On the top of the stabilization fabric should be another layer of material that is somewhat finer than the sub base material. This material will still allow the percolation of water, but will also provide a nice even, smooth sub base for the initial asphalt layer. This material should be compacted and rolled to achieve a compaction of at least 95%. A testing agency should be employed to take compaction tests and ensure that the compaction reaches levels over the required 95%. The moisture content of this material is also a component of its ability to compact. The moisture content will be analyzed and measured by the testing lab on the site.
- The actual driveway should consist of two separate layers of asphalt, installed separately. The initial layer of asphalt should be a minimum of 1 1/2 inches, but preferably 2 inches or more. The heavier the initial layer of asphalt, the stronger and more reliable will be the final driveway application. The second layer, or the wearing layer of asphalt should be at least 1 ½ inches of material, compacted and rolled. A local, competent driveway contractor should be hired to perform this work. It is recommended that research and due diligence be performed to ensure that the selection of the driveway contractor is proper.
- The final result should be an even, well-pitched and consistent layering of asphalt material resulting in a uniform surface, without inconsistencies in grade and without the appearance of individual particles of asphalt. Proper asphalt surfaces should not appear porous and each individual grain of asphalt should not be obviously exposed on the surface of the drive. If the asphalt appears to be a gathering of particles, it is not compacted and installed properly. This must be corrected due to the accumulation of water within the openings between the asphalt particles and the freeze and thaw negative effects to this type of asphalt installation.
Existing driveway repair
If you already have an existing driveway, the following inspection should be performed.
- Review the condition of the surface of the asphalt. The surface should be consistent and without substantial cracking and splitting. Any cracks and splits in the driveway should be evaluated for depth and width.
- If there are not noticeable depressions in the driveway that are holding water, and the only issues appear to be cracks and crevices in the drive, these should be filled with a driveway, asphalt product that is specifically designed for this repair. This asphalt material can be found at any hardware store or any of the big box, builder supply stores.
- The repair of cracks and crevices within the asphalt surface is similar to the repair of cracks in any type of rigid surface, such as concrete and masonry. The repair should start with the total and complete cleaning of the crack or crevice in the asphalt. This cleaning should consist of blowing the debris out of the crevice with either a leaf blower or a concentrated air compressor. Once the area is cleaned, there is usually a primer that is brushed into the crack and crevice to promote the adhesion of the asphalt filler material. The instructions for the repair of the asphalt should be followed in accordance with the manufacturer’s recommendation for this repair.
- If the inspection of the existing driveway resulted in the identification of several depressions or other areas of obvious structural failure, then these areas will have to be dealt with.
- The removal of the existing area that is causing the depression or the inconsistency in the asphalt surface must be performed. This removal should be accomplished by either cutting the existing asphalt and excavating the area that is compromised, or actually chopping out the asphalt with a jackhammer. If this becomes the extent of the correction, it is recommended that a professional contractor be hired to perform this work.
In some instances, the inspection of the existing driveway structure results in the evaluation that the entire drive has been compromised or was not installed in the correct fashion. If it is determined that the entire surface of the asphalt is damaged, and cannot be properly corrected by the local removal of sections, then the entire removal of the driveway is recommended.
If the entire removal of the driveway is required, then obviously this is work for the professional contractor that is experienced in driveway replacement and repair. Of specific importance are the following issues.
- The drainage of the replaced driveway must be consistent with the positive drainage patterns required to shed the water away from the structure to an area that will accept the water without collection and causing other issues of water accumulation.
- The sub base of the replaced driveway must be carefully constructed to ensure that the sub base is consistent with the need to properly structurally support the new layers of asphalt. If the existing drive has failed, it has failed for a reason and the correction of the sub base is essential to the proper construction of the new driveway.
- If the existing driveway is being replaced, then there is the opportunity to change the direction and the ultimate layout of the driveway. This is the time for the property owner to take advantage of the chance to revise any layout to their individual convenience.
- This is also the opportunity to add to the surface area of the driveway. If additional parking is required for vehicles, or another area is required to be asphalted for deliveries or ease of turning, then this is the opportunity for the property owner to resolve any of these issues.
In summary, the driveway is an important element to the home and to the structure. The proper installation of the driveway must be consistent with the proper installation of the sub base as well as the asphalt topping layers with a well-draining surface. Remember that the sub base and the drainage are the keys to the entire establishment of a driveway that will hold up to constant vehicle traffic and weather conditions.
Drainage, base material and proper layering of the asphalt are the keys to a driveway that will offer consistent and structurally stable access to your home and property.