# Optimizing the Performance of Window Frames: A Comprehensive Review of Materials in China
## 3 Improvement Methods and Sustainability Assessment
### Sustainability Assessment
In general fires, the combustion deformation of doors and windows in buildings poses a more serious threat to life than the combustion of building structures. According to GB/T 8624-2006 [151] Classification of Burning Performance of Building Materials and Products, the average temperature of a general building fire is between 700 and 900 \({}^{\circ}\)C, and wood is usually carbonized at a rate of 0.64 mm per minute. The carbonization layer naturally isolates the wood from the outside world and increases the temperature that the wooden components can withstand. If the aluminum-clad wooden window frame is exposed to an open flame at 800 \({}^{\circ}\)C for 30 min, only 19 mm will be carbonized. The integrated materials in the aluminum-clad wooden window have undergone certain flame-retardant treatment during the processing, which plays a better role in fire prevention and disaster reduction. Life expectancy  
Durability or lifespan depends on the use of appropriate products, correct installation, and regular maintenance [152; 153; 154]. During the installation of window frames, efforts should be made to avoid damaging the original building structure and to pay attention to whether the installation process complies with regulations. In this sense, knowledge regarding the service life of window frames is extremely relevant, aiding the adoption of adequate solutions in the design and maintenance stages. In terms of window frame life prediction, the service life prediction methods are divided into three main groups [155]: deterministic (e.g., factor and graphical method); probabilistic (e.g., Markov chains); and engineering methods (e.g., failure modes effects analysis (FMEA)). Combined with the actual case of Portugal, [PERSON] et al. [156] analyzed 173 samples of aluminum window frames and 41 samples of wood window frames and proposed a prediction model for the service life of aluminum window frames and wood window frames based on the factor method, which added additional value to the revision of the ISO 15686-1 [157] standard. [PERSON] et al. [137] evaluated and analyzed the degradation of 182 window frames (including aluminum, wood, and PVC) under real-use conditions and environmental exposure, and established a window frame degradation model, which reflected the evolution law of window frame degradation with time. In a simplified approach, the standard for durability and the different European EPD operators [136; 156] specify that window frames must present an estimated service life of at least 30 years. In installation and maintenance, at present, the installation grade requirements of building exterior windows are mainly based on the current national standard GB/T 7106 [158] in classifying and testing their air tightness, water tightness, and wind pressure resistance. [PERSON] et al. [135] conducted a study indicating that aluminum alloy window frames, apart from being cleaned for aesthetic reasons, have lower maintenance costs. Coatings, anodization, and other treatments can extend their lifespan. Specifically, anodized aluminum alloys can endure for over 20 years in harsh environments. On the other hand, PVC window frames encounter issues in maintenance primarily due to their surface vulnerability; scratches caused by hard particles can affect their appearance and durability. Recommended maintenance methods for PVC frames include using non-alkaline cleaners for regular cleaning, suggested every six months, as repair are difficult once the frame is damaged. Maintenance costs for wooden window frames are relatively high, requiring periodic coatings to maintain appearance and provide resistance against weathering and degradation. Typically, exterior painting is recommended every 5 years and staining every 3 years. Aluminum-clad wooden frames generally cost 14-18% more than pure wooden frames, but they incur lower external maintenance costs due to the stability provided by the aluminum cladding, which lasts for an extended period.